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Measurement uncertainties in clinical chemistry are commonly regarded as heteroscedastic - having a constant relative standard deviation irrespective of the concentration of the measurand. The uncertainty is usually determined at two concentrations using stabilized control materials and assumed to represent the analytical goal. The purpose of the present study was to use duplicates of unselected patient samples to calculate the absolute and relative repeatability component of the intra-laboratory measurement uncertainty from duplicates, using the Dahlberg formula and analysis of variance components. Estimates were made at five different concentration intervals of ALT, AST, Calcium, Cholesterol, Creatinine, CRP, Triglycerides and TSH covering the entire concentration interval of the patient cohort. This partioning allows detailing their repeatability profiles. The calculations of the profiles were based on randomly selected results from sets of duplicates ranging from 12,000 to 65,000 pairs. The repeatability of the measurands showed substantial variability within the measuring interval. Therefore, characterizing imprecision profiles as purely homo- or heteroscedastic or by a single number may not be optimal for the intended use. The present data make a case for nuancing the evaluation of analytical goals and minimal differences of measurement results by establishing uncertainty profiles under repeatability conditions, using natural patient samples. Funding Agencies|Karolinska university laboratory; County council of Ostergotland

Measurement uncertainty (MU) can be estimated and calculated by different procedures, representing different aspects and intended use. It is appropriate to distinguish between uncertainty determined under repeatability and reproducibility conditions, and to distinguish causes of variation using analysis of variance components. The intra-laboratory MU is frequently determined by repeated measurements of control material(s) of one or several concentrations during a prolonged period of time. We demonstrate, based on experimental results, how such results can be used to identify the repeatability, pure reproducibility and intra-laboratory variance as the sum of the two. Native patient material was used to establish repeatability using the Dahlberg formula for random differences between measurements and an expanded Dahlberg formula if a non-random difference, e.g. bias, was expected. Repeatability and reproducibility have different clinical relevance in intensive care compared to monitoring treatment of chronic diseases, comparison with reference intervals or screening. Funding Agencies|Karolinska university laboratory; County council of Ostergotland

Introduction The use of glucose point-of-care testing (POCT) devices for the diagnosis of diabetes mellitus (DM) is an ongoing controversy. In patient management, glucose concentrations are determined by POCT and core laboratory glucose methods, and the values are commonly compared even though the samples collected are different, namely, capillary whole blood and venous plasma. In individual patients it is difficult to distinguish between factors that can influence the results, such as sample type and measuring procedure. In this study, glucose concentrations obtained using POCT and core laboratory instruments were assessed to duplicate typical scenarios experienced in healthcare. Corresponding diagnosis rates of impaired glucose tolerance (IGT) and DM based on fixed, method-independent cutoffs were compared. Methods Glucose concentration was measured by the 2-h oral glucose tolerance test (OGTT) in samples collected from an inpatient cohort and a cohort from the general population. Two POCT methods, namely, a handheld unit-use glucometer and a small bench-top analyzer with batch reagents, and two core laboratory procedures were used to measure glucose concentrations. The sample types were whole blood and plasma samples collected from venous and capillary blood. The glycated hemoglobin level in whole blood was also determined. Results A total of 231 subjects were included in the study. The 2-h OGTT glucose concentrations in the capillary whole blood samples showed a positive bias of 0.8 mmol/L compared to those obtained using core laboratory plasma glucose methods, leading to increased rates of diabetes diagnosis. This bias decreased to 0.2 mmol/L when venous blood was used in the tests. A change in the method used by the core laboratory introduced a negative bias of 0.5 mmol/L and, consequently, a lower diagnosis rates. Discussion and Conclusion Venous blood samples measured at the point-of-care are the most suitable sample type for the measurement of the glucose concentration in the 2-h OGTT. The investigated unit-use POCT method is suitable for the diagnosis of IGT and DM when venous blood samples are collected. Importantly, changes in measurement procedures can introduce a bias and affect diagnosis rates, thereby emphasizing the need for further harmonization of glucose methods. Plain Language Summary A plain language summary is available for this article. Electronic supplementary material The online version of this article (10.1007/s13300-018-0495-0) contains supplementary material, which is available to authorized users., Plain Language Summary In clinical practice, a physician may be confronted with blood glucose concentrations determined using different devices. It is difficult for the treating physician to assess the effect of factors that can impact the glucose measurement, such as sample type and measuring procedure, for a given glucose concentration result. The aim of this study was to duplicate typical scenarios in the healthcare setting in terms of differences in glucose concentrations in capillary and venous samples obtained using a handheld point-of-care testing device, one benchtop device, and two core laboratory instruments. The diagnosis rates of impaired glucose tolerance and diabetes mellitus were compared to demonstrate the effects of the glucose concentrations measured using these different devices in terms of clinical response. We performed an oral glucose tolerance test and obtained the blood glucose concentration immediately before and 2 h after an oral glucose load. The results were compared and presented using difference and scatter plots. A total of 231 subjects were included in the study. Glucose concentrations in capillary whole blood samples showed a positive bias compared to those determined using core laboratory methods, leading to increased rates of diabetes diagnosis. This bias decreased when venous whole blood samples were used. A change in the method used in the core laboratory introduced a negative bias and, consequently, lower diagnosis rates. Changing laboratory devices can introduce a bias that is sufficiently large as to affect the diagnosis of diabetes since the latter is based on method-independent cutoffs. From these findings we conclude that both of the point-of-care devices investigated are suitable for the diagnosis of diabetes when venous samples are used. Our findings also emphasize the need for further harmonization of the glucose testing method. Electronic supplementary material The online version of this article (10.1007/s13300-018-0495-0) contains supplementary material, which is available to authorized users.

Essentials Age-adjusted D-dimer cut-offs decrease the false positives in the elderly. Four D-dimer assays were compared in venous thromboembolism outpatients in an emergency ward. Age-adjusted cut-off resulted in improved specificity with maintained sensitivity for all assays. There was a substantial decrease in false positive results, especially in the older population. SUMMARY Background The study compares different D-dimer assays and age-adjusted cut-offs in outpatients with suspected venous thromboembolism (VTE). The plasma concentration of this sensitive biomarker is increased by activated coagulation, but also by several conditions that are linked to an increased risk of VTE. One such condition is old age, which poses a common clinical problem where many prefer not to analyze D-dimer in elderly patients. Age-adjusted cut-offs have been validated for both deep venous thrombosis (DVT) and pulmonary embolism, aiming to increase specificity without notably decreasing sensitivity. Objectives We evaluated four common D-dimer assays in parallel, with and without applying age-adjusted cut offs for VTE. Patients/methods The prospective single-center study was conducted in 940 outpatients attending the emergency department with clinically suspected pulmonary embolism or DVT. Four automated D-dimer assays were compared (Siemens INNOVANCE® , Roche Tina-quant, Medirox MRX and STA® -Liatest® D-Di PLUS). Results All assays performed with areas under the ROC curve (AUC) > 0.9 and maintained their sensitivities after implementation of age-adjusted cut-offs. Specificities increased by 6-7% and number needed to test decreased by < 0.3. The rate of false positive results decreased by 6% overall and by 10-20% for patients ≥ 70. Conclusions Age-adjusted cut-offs resulted in maintained high sensitivity and a modest improvement in specificity and number needed to test for all evaluated D-dimer assays. There was a significant reduction in false positive results, which reflects avoidable unnecessary imaging without any compromise of clinical safety. This suggests a potential to benefit the management of VTE in elderly patients, both clinically and economically.

Dr. Sadler has very kindly commented our report ‘Measurement repeatability profiles of eight frequently requested measurands in clinical chemistry determined by duplicate measurements of patient sa...

Measurement imprecision is usually calculated from measurement results of the same stabilized control material(s) obtained over time, and is therefore, principally, only valid at the concentration(s) of the selected control material(s). The resulting uncertainty has been obtained under reproducibility conditions and corresponds to the conventional analytical goals. Furthermore, the commutability of the control materials used determines whether the imprecision calculated from the control materials reflects the imprecision of measuring patient samples. Imprecision estimated by measurements of patient samples uses fully commutable samples, freely available in the laboratories. It is commonly performed by calculating the results of routine patient samples measured twice each. Since the duplicates are usually analysed throughout the entire concentration interval of the patient samples processed in the laboratory, the result will be a weighted average of the repeatability imprecision measured in the chosen measurement intervals or throughout the entire interval of concentrations encountered in patient care. In contrast, the uncertainty derived from many measurements of control materials over periods of weeks is usually made under reproducibility conditions. Consequently, the repeatability and reproducibility imprecision play different roles in the inference of results in clinical medicine. The purpose of the present review is to detail the properties of the imprecision calculated by duplicates of natural samples, to explain how it differs from imprecision calculated from single concentrations of control materials, and to elucidate what precautions need to be taken in case of bias, e.g. due to carry-over effects.

Introduction The diagnosis of diabetes mellitus is based on suitable cut-off values of specific biomarkers, such as the concentration of glucose in plasma. The German Diabetes Association has very recently published a clinical practice guideline on the definition, classification and diagnosis of diabetes mellitus that recommends measurements of plasma glucose concentration have an imprecision defined as a minimal difference (MD) of at a fasting plasma glucose concentration of 7.0 mmol/L. To obtain reliable values for the MD, we investigated long-term and short-term measurement uncertainty. Methods The imprecision was determined by two approaches: (1) a long-term dataset with imprecision based on the Guideline of the German Medical Association on Quality Assurance in Medical Laboratory Examinations (Rili-BAEK), in a medical laboratory operating 24/7, using internal quality control (IQC) data for four concentrations during a 10-year period; and (2) a detailed short-term dataset with imprecision assessed by hourly measurements of control materials. These datasets were used to calculate the MD cut-off (MDcut-off) as: \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ {\text{MD}}_{\text{cut-off}} = k \times {\text{SD}} $$\end{document}MDcut-off=k×SD = 2 \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ \times {\text{SD}} $$\end{document}×SD, where SD is the standard deviation and k = 2 represents a confidence level of 95%. Results The MDcut-off of ≤ 0.7 mmol/L at a fasting plasma glucose concentration of 7.0 mmol/L (MDcut-off 7.0) for the long-term and the short-term approaches were 0.44 and 0.40 mmol/L, respectively. The MDcut-off 7.0 from both approaches was therefore below the recommended value of 0.7 mmol/L. It was noted that the variability in performance within and between instruments can be covered by reporting the long-term MDcut-off 7.0 across all connected instruments. In this study, stable results for the MDcut-off 7.0 were obtained after 1 year. Conclusion Imprecision as measured by IQC data is remarkably stable over many years of operation. Current imprecision assessment usually focuses on only single instruments, whereas clinicians perceive the measurement as the result of the combined analytical performance of all instruments used for a certain assay. In the clinical setting, the MD may be a more useful measure of imprecision, and we suggest deriving the MDcut-off combined from all instruments and control cycles that are used in the patient care setting for a given analyte. Electronic supplementary material The online version of this article (10.1007/s13300-019-00740-w) contains supplementary material, which is available to authorized users.

There is an emerging interest in the diverse functions of neutrophil extracellular traps (NETs) in a variety of disease settings. However, data on circulating NETs rely largely upon surrogate NET markers such as cell-free DNA, nucleosomes, and NET-associated enzymes. Citrullination of histone H3 by peptidyl arginine deiminase 4 (PAD4) is central for NET formation, and citrullinated histone H3 (H3Cit) is considered a NET-specific biomarker. We therefore aimed to optimize and validate a new enzyme-linked immunosorbent assay (ELISA) to quantify the levels of H3Cit in human plasma. A standard curve made of in vitro PAD4-citrullinated histones H3 allows for the quantification of H3Cit in plasma using an anti-histone antibody as capture antibody and an anti-histone H3 citrulline antibody for detection. The assay was evaluated for linearity, stability, specificity, and precision on plasma samples obtained from a human model of inflammation before and after lipopolysaccharide injection. The results revealed linearity and high specificity demonstrated by the inability of detecting non-citrullinated histone H3. Coefficients of variation for intra- and inter-assay variability ranged from 2.1 to 5.1% and from 5.8 to 13.5%, respectively, allowing for a high precision. Furthermore, our results support an inflammatory induction of a systemic NET burden by showing, for the first time, clear intra-individual elevations of plasma H3Cit in a human model of lipopolysaccharide-induced inflammation. Taken together, our work demonstrates the development of a new method for the quantification of H3Cit by ELISA that can reliably be used for the detection of NETs in human plasma.

Introduction: Duplicate measurements can be used to describe the performance and analytical robustness of assays and to identify outliers. We performed about 235,000 duplicate measurements of nine routinely measured quantities and evaluated the observed differences between the replicates to develop new markers for analytical performance and robustness. Materials and methods: Catalytic activity concentrations of aspartate aminotransferase (AST), alanine aminotransferase (ALT), and concentrations of calcium, cholesterol, creatinine, C-reactive protein (CRP), lactate, triglycerides and thyroid-stimulating hormone (TSH) in 237,261 patient plasma samples were measured in replicates using routine methods. The performance of duplicate measurements was evaluated in scatterplots with a variable and symmetrical zone of acceptance (A-zone) around the equal line. Two quality markers were established: 1) AZ95: the width of an A-zone at which 95 % of all duplicate measurements were within this zone; and 2) OPM (outliers per mille): the relative number of outliers if an A-zone width of 5 % was applied. Results: The AZ95 ranges from 3.2% for calcium to 11.5% for CRP and the OPM from 5 (calcium) to 250 (creatinine). Calcium, TSH and cholesterol have an AZ95 of less than 5% and an OPM of less than 50. Conclusions: Duplicate measurements of a large number of patient samples identify even low frequencies of extreme differences and thereof defined outliers. We suggest two additional quality markers, AZ95 and OPM, to complement description of assay performance and robustness. This approach can aid the selection process of measurement procedures in view of clinical needs.

Simulations play an increasing role in metrology and analytical chemistry, particularly the use of simulated normal distributions. Microsoft Excel is available to almost everybody and normal distributions can be simulated using either an innate function or other algorithms. We explore the success of five different algorithms to simulate normal distributions and compare the outcome with a simulation coded in R. The normality of 106 data points simulated by the chosen algorithms was tested by different recognized statistical procedures and Q–Q plots. They all failed the statistical procedures, but evaluating the Q–Q plots revealed different types of deviations. It also showed that the deviations, although statistically significant, most likely do not have any practical relevance in laboratory work.

Background: The innovative pneumatic tube system (iPTS) transports one sample at a time without the use of cartridges and allows rapid sending of samples directly into the bulk loader of a laboratory automation system (LAS). We investigated effects of the iPTS on samples and turn-around time (TAT). Methods: During transport, a mini data logger recorded the accelerations in three dimensions and reported them in arbitrary area under the curve (AUC) units. In addition representative quantities of clinical chemistry, hematology and coagulation were measured and compared in 20 blood sample pairs transported by iPTS and courier. Results: Samples transported by iPTS were brought to the laboratory (300 m) within 30 s without adverse effects on the samples. The information retrieved from the data logger showed a median AUC of 7 and 310 arbitrary units for courier and iPTS transport, respectively. This is considerably below the reported limit for noticeable hemolysis of 500 arbitrary units. Conclusions: iPTS reduces TAT by reducing the hands-on time and a fast transport. No differences in the measurement results were found for any of the investigated 36 analytes between courier and iPTS transport. Based on these findings the iPTS was cleared for clinical use in our hospital.

Simulations are used in many calculations and forecasting procedures, from market analysis to estimation of measurement uncertainty. Microsoft Excel offers an innate procedure to simulate a Gaussian distribution and a pseudorandom number generator (PRNG). Using the latter, five additional simulations models with a potential to simulate the normal probability distribution function (PDF) were explored and compared with the theoretical Gaussian PDF based on a defined average (location) and standard deviation (width). The simulated distributions appeared “displaced” from the Gaussian function. Simulations of the distributions by a large number of observations confirmed different properties of the six simulation procedures. The range of the distributions differed, i.e. the difference between the maximum and minimum simulated values. The innate procedure yielded an unsymmetrical distribution that was shifted to the right (higher values). A miniscule divergence from expected values was demonstrated. A systematic difference between the simulated distributions and the theoretical Gauss distribution may not be of any practical importance in applied metrology, whereas it may be devastating in other applications, e.g. encoding and market simulations. There were differences between the models which may influence their use. It is suggested that a root cause may be found in the PRNG.

Zusammenfassung Einleitung: Die Leistungsfähigkeit von Messverfahren in medizinischen Laboratorien wird im Allgemeinen überwacht durch das regelmäßige Messen von einem oder mehreren Qualitätskontrollmaterialien, sogenannten internen Qualitätskontrollen. Die Bewertung des Messergebnisses der Qualitätskontrolle führt zur Annahme oder zur Sperrung von Patientenmessergebnissen und erfolgt gemäß anerkannten Regeln und gesetzlicher Vorgaben. Methoden: Varianzen von Qualitätskontrollmessungen sowie die Zielwerte für die Westgardauswertung wurden während einer ersten Phase (Vorperiode) ermittelt. In der darauf folgenden zweiten Phase (Messphase) wurden die Qualitätskontrollergebnisse gemäß der deutschen Rili-BÄK und gemäß den Westgard 1:2s und 1:3s Regeln für vier beispielhaft ausgewählte Messverfahren verglichen, die folgende Charakteristika aufwiesen: Geringe Unpräzision und geringe Unrichtigkeit (Glukose im Plasma), große Unpräzision und geringe Unrichtigkeit (Phenobarbital im Serum), geringe Unpräzision und große Unrichtigkeit (Natrium im Urin) sowie große Unpräzision und große Unrichtigkeit (Magnesium im Plasma). Ergebnisse: Das Ergebnis der Bewertung gemäß der Westgard-Regeln (1:2s und 1:3s) ist stark abhängig von der Vorperiode, wohingegen die Bewertung durch die Rili-BAEÄK auf den einheitlich vorgegebenen Grenzen und den bindenden Zielwerten beruht. Die Anzahl der Grenzverletzungen, die von der Rili-BÄK bzw. den Westgard 1:2s und 1:3s Regeln erkannt wurden, unterscheiden sich zum Teil deutlich. Die Rili-BÄK Grenzen für die Plasma-Glukose erscheinen großzügig vor dem Hintergrund der Leistungsfähigkeit des verwendeten Messverfahrens. Schlussfolgerung: Durch die definierten Zielwerte und Bewertungsgrenzen hat die Rili-BÄK das Potential, die Harmonisierung von Patientenergebnissen klinisch-chemischer Untersuchungen, die in unterschiedlichen Laboratorien erstellt werden, zu verbessern. Laboratorien, die gemäß der Westgard-Regeln eine Bewertung der internen Qualitätskontrolle durchführen und Zielwerte und Bewertungsgrenzen demzufolge intern und unabhängig von anderen Laboratorien ermitteln, müssen sich für die Harmonisierung von Patientenergebnissen auf die externe Qualitätskontrolle verlassen.

Medicine is diagnosis, treatment and care. To diagnose is to consider the probability of the cause of discomfort experienced by the patient. The physician may face many options and all decisions are liable to uncertainty to some extent. The rational action is to perform selected tests and thereby increase the pre-test probability to reach a superior post-test probability of a particular option. To draw the right conclusions from a test, certain background information about the performance of the test is necessary. We set up a partially artificial dataset with measured results obtained from the laboratory information system and simulated diagnosis attached. The dataset is used to explore the use of contingency tables with a unique graphic design and software to establish and compare ROC graphs. The loss of information in the ROC curve is compensated by a cumulative data analysis (CDA) plot linked to a display of the efficiency and predictive values. A standard for the contingency table is suggested and the use of dynamic reference intervals discussed.

Error methods – compared with uncertainty methods – offer simpler, more intuitive and practical procedures for calculating measurement uncertainty and conducting quality assurance in laboratory medicine. However, uncertainty methods are preferred in other fields of science as reflected by the guide to the expression of uncertainty in measurement. When laboratory results are used for supporting medical diagnoses, the total uncertainty consists only partially of analytical variation. Biological variation, pre- and postanalytical variation all need to be included. Furthermore, all components of the measuring procedure need to be taken into account. Performance specifications for diagnostic tests should include the diagnostic uncertainty of the entire testing process. Uncertainty methods may be particularly useful for this purpose but have yet to show their strength in laboratory medicine. The purpose of this paper is to elucidate the pros and cons of error and uncertainty methods as groundwork for future consensus on their use in practical performance specifications. Error and uncertainty methods are complementary when evaluating measurement data.

It is an established procedure in laboratories to verify measurement methods by comparison of results from patient samples (split sample). The information retrieved and evaluated from a comparison is often limited to a scatter plot, a regression analysis and a differential plot. However, many more features and performance criteria are available from the same data. Access to a comprehensive set of information can also be used to harmonize results by recalibration and estimate any risk in applying alternate methods or surrogates to reference methods. Common principles for comparison of results are explained. Well known and new relations between commonly used methods and their limitations are discussed. A new application of the empirical folded density functions is introduced, and the use of a simplified error grid in the evaluation of a comparison is explored. Parametric and nonparametric pairwise significance tests and a convenient option of partitioning and limiting the dataset, ordinary linear and Deming regression functions, including uncertainties of the constants are provided in an Excel spreadsheet that is submitted as a downloadable supplemental file. The information harboured in a split sample comparison of methods is explored in detail. Procedures cover the main content of CLSI recommendations EP9, EP21 and EP27. Several additional practical procedures are described in a submitted single spreadsheet program.

Background: The IFCC Task Force on Clinical Applications of Cardiac Biomarkers suggests comparing several contemporary sensitive troponin assays in the same, sufficiently large reference population. Methods: Three contemporary sensitive assays were used to measure troponin I concentration in samples from a uniquely large healthy population (2404 individuals) and in a sub-group with tighter inclusion criteria of 908 individuals. The 99th percentiles were calculated using quantile regression which takes the entire population into account. Results: The 99th percentile for the ARCHITECT STAT Troponin I assay was 21 ng/L, 31 ng/L for the ADVIA Centaur Troponin I-Ultra assay and 28 ng/L for the Dimension Vista cTnI assay. Significantly higher values were found in males than in women only in the Dimension Vista cTnI assay and in the subgroup for the ARCHITECT STAT Troponin I assay. Conclusions: Quantile regression provides a tool to accurately estimate the 99th percentile and establish a continuous function of the relation between the 99th percentile and the age and gender. There was no age dependency demonstrated. A gender difference was found in one assay but inconclusive in another and not demonstrated in a third.

Background A logical consequence of the introduction of robotics and high-capacity analysers has seen a consolidation to larger units. This requires new structures and quality systems to ensure that laboratories deliver consistent and comparable results. Methods A spreadsheet program was designed to accommodate results from up to 12 different instruments/laboratories and present IQC data, i.e. Levey-Jennings and Youden plots and comprehensive numerical tables of the performance of each item. Input of data was made possible by a ‘data loader’ by which IQC data from the individual instruments could be transferred to the spreadsheet program on line. Results A set of real data from laboratories is used to populate the data loader and the networking software program. Examples are present from the analysis of variance components, the Levey-Jennings and Youden plots. Conclusions This report presents a software package that allows the simultaneous management and detailed monitoring of the performance of up to 12 different instruments/laboratories in a fully interactive mode. The system allows a quality manager of networked laboratories to have a continuous updated overview of the performance. This software package has been made available at the ACB website.

The majority of subarachnoid hemorrhage (SAH) is diagnosed using imaging techniques. The sensitivity of computed tomography scans decreases with increasing time after the bleeding event which can lead to false negative CT scans. Spectrophotometry and microscopic investigations of the cerebrospinal fluid (Csf) can provide additional diagnostic support, but may not be available for emergency diagnoses. Csf-Ferritin has been suggested as an alternative additional marker for SAH that present late and has a potency to be measured in a routine laboratory.A routine Ferritin chemiluminescent assay (Dimension Vista) was compared with a branded and CE-marked Csf-Ferritin nephelometric assay (BN ProSpec) using surplus routine patient samples. We calculated imprecision at pertinent concentrations, compared patient samples, and established reference intervals.The standard deviation was about a third for the Dimension Vista assay compared to that of the BN ProSpec assay at the three tested concentrations. The correlation showed a systematic difference between the methods but the correlation was high (r = 0.955). Accordingly, the reference intervals were higher for the BN ProSPec (2.7-16.8 μg/L) than for the Dimension Vista (2.0-12.6 μg/L).The precision of the Dimension Vista measurements was considerably better than that of the BN ProSpec. The Dimension Vista results correlated well with those of the comparative method, yielding slightly lower values. This is reflected in the reference intervals. These findings permit the use of the routinely available Ferritin assay of the Dimension Vista for measuring Csf-Ferritin and complementing the late diagnosis of SAH outside office hours of specialized Csf laboratories.

Results of measurements of quantities in laboratory medicine are used for diagnosis, prediction and monitoring of disease. Evaluation of results is based on evidence and practical experience. In both cases consistency and transferability of results is needed. For diagnosis and prediction a result is compared to a reference value or reference interval whereas in monitoring it is more important to compare results of measurements with previous results. The analytical goals may therefore vary depending on the intended use of the results and both trueness and precision will need to be considered. The analytical goals may also be influenced by the disease characteristics. A brief review of available methods and principles will be given.

The von Willebrand factor (VWF) is elevated in patients with diabetes mellitus and degraded by a metalloprotease, ADAMTS13. We hypothesized that this elevation is due to a decreased function of ADAMTS13. Thus, we investigated ADAMTS13 in patients with diabetes mellitus without and with peripheral artery occlusive disease (PAOD). When treating the latter group with dalteparin, VWF is reported to increase significantly, and we therefore measured ADAMTS13 also in these patients. VWF antigen and ADAMTS13 antigen and activity concentrations were measured in patients with diabetes mellitus but without PAOD (diabetes mellitus; n = 23) and with diabetes mellitus and PAOD (diabetes mellitus + PAOD; n = 65) before and after treatment with dalteparin or placebo. In the diabetes mellitus group, concentration of VWF antigen was significantly higher, whereas that of ADAMTS13 activity was significantly lower than in the healthy controls. In the diabetes mellitus along with PAOD group, VWF antigen was significantly higher, but ADAMTS13 antigen or activity did not differ significantly from those of healthy controls. The ADAMTS13 activity/antigen ratio was lower than in controls only in the diabetes mellitus patient group. VWF antigen increased significantly during dalteraprin treatment, whereas ADAMTS13 activity and antigen remained unchanged. Only patients with diabetes mellitus had significantly lower concentrations of ADAMTS13 activity in plasma than controls, although the diabetes mellitus along with PAOD had a more pronounced VWF antigen elevation than diabetes mellitus patients, illustrating a possible link between ADAMTS13 and microangiopathy in diabetes mellitus patients. The increase in VWF antigen concentration during treatment with dalteparin does not seem to be due to changes in ADAMTS13.

The diagnostic performance of six methods for bacteriuria testing has been studied in 781 urine specimens obtained in primary health care, using conventional culture as reference method. The cut-off limits for classification of test results into positive and negative have been optimized with respect to diagnostic performance in primary health care. With optimized tests the following diagnostic efficiencies were obtained: 1) Bacterial ATP, 0.94; 2) Bacterial count in sediment, 0.93; 3) Nitrite test, 0,92; 4) Dipslide test, 0,92; 5) White cell count in sediment; 0,87; 6) Granulocyte esterase test; 0.83. The diagnostic performance was also studied for all combinations of two tests. The highest diagnostic efficiency (0.96) was obtained by combining the ATP and dipslide tests. High diagnostic efficiencies can be obtained by a rapid primary test, using other tests for follow-up testing of specimens with intermediate or uninterpretable primary results. The most promising results were obtained by using ATP as the primary test, with follow-up testing of specimens with 3–25 nmol/l of ATP (12 per cent of the specimens). Follow-up testing by conventional culture resulted in overall diagnostic efficiency of 0.98. By performing the nitrite test on specimens with intermediary ATP-results, 81 per cent of the patients with UTI can be classified without culture. Only patients with intermediary ATP and negative nitrite results (10 per cent of the total number) will have to wait for final diagnosis based on conventional culture. Some alternative strategies to combine available methods are discussed in detail. Major advantages of the ATP test are that the test can be performed while the patients are waiting; it provides a numerical and objective result, and, in contrast to culture, it is not influenced by adhesion of bacteria to somatic cells.

This study aimed at validating common bootstrap algorithms for reference interval calculation.We simulated 1500 random sets of 50-120 results originating from eight different statistical distributions. In total, 97.5 percentile reference limits were estimated from bootstrapping 5000 replicates, with confidence limits obtained by: (a) normal, (b) from standard error, (c) bootstrap percentile (as in RefVal) (d) BCa, (e) basic, or (f) student methods. Reference interval estimates obtained with ordinary bootstrapping and confidence intervals by percentile method were accurate for distributions close to normality and devoid of outliers, but not for log-normal distributions with outliers. Outlier removal and transformation to normality improved reference interval estimation, and the basic method was superior in such cases. In conclusions, if the neighborhood of the relevant percentile contains non-normally distributed results, bootstrapping fails. The distribution of bootstrap estimates should be plotted, and a non-normal distribution should warrant transformation or outlier removal.

Pre-eclampsia is associated with both maternal and foetal complications. Several studies have shown increased trophoblast apoptosis in the placenta of women with this condition. The aim of this study was to investigate whether increased apoptosis can be detected as elevated levels of an apoptotic product in serum samples from women with pre-eclampsia. For this purpose, we used the M30-Apoptosense ELISA assay, which measures a neo-epitope of cytokeratin 18 that is exposed after cleavage by caspases during apoptosis of epithelial cells (M30 antigen). The M30-antigen concentrations were measured in the sera of 15 healthy pregnant women and 15 patients with pre-eclampsia (gestation weeks 24-34). Patients with pre-eclampsia had significantly higher serum M30-antigen concentrations, median 120 U/L, compared to 15 healthy pregnant women matched for pregnancy length, median 104 U/L (p = 0.01). This is consistent with previous findings of increased trophoblast apoptosis in women with pre-eclampsia and raises the possibility that M30-antigen can be used as a serum marker for the severeness of this condition for the mother and child.

There is a great need to evaluate renal function regularly in elderly people. This study aimed at analyzing renal function in stable, community-dwelling elderly people of 75 years and over, to compare measured and predicted glomerular filtration rates (GFR) and to develop an accurate prediction equation for this age group.Forty-five ambulatory elderly people in stable health in ordinary living were randomly selected into four age-classes, aged 75-95. Demographic data, personal activities of daily living, continuous drug prescriptions, body composition, blood pressure and blood chemistry were analysed. GFR was measured as Iohexol clearance based on three time-points 3, 4 and 7 hours after Iohexol injection.Mean GFR was well preserved in all four age-classes. The GFR range was 18-83 mL/min and declined with age. The Cockcroft-Gault prediction equation systematically underestimated measured GFR. A new 'GFRA' prediction equation is presented, based on the inverse of serum cystatin C and independent of gender, body surface area, body weight, lean body mass or serum creatinine. The proposed equation underestimated measured GFR with a mean of only 0.1 mL/min, had better precision compared with the Cockcroft-Gault equation, and was evaluated by the method of cross-validation.GFR exhibits extensive heterogeneity in frail, community-dwelling elderly people. The proposed GFRA was clearly more precise than the Cockcroft-Gault prediction equation in the study group. However, it needs to be validated in a larger population of elderly subjects, including more individuals in stable health with substantially reduced renal function in whom GFR is measured by a reference method with adequate sampling time.

The use of MDRD-eGFR to diagnose Chronic Kidney Disease (CKD) is based on the assumption that the algorithm will minimize the influence of age, gender and ethnicity that is observed in S-Creatinine concentration and thus allow a single cut-off at which further diagnostic and therapeutic actions should be considered. This hypothesis is tested in a retrospective analysis of outpatients (N=93,404) and hospitalised (N=35,572) patients in UK and Sweden, respectively. An algorithm based on the same model as the MDRD-eGFR algorithm was derived from simultaneously measured S-Creatinine concentrations and Iohexol GFR in a subset of 565 patients. The combined uncertainty of using this algorithm was estimated to about 15 % which is about three times that of the S-Creatinine concentration results. The diagnostic performance of S-Creatinine concentration was evaluated using the Iohexol clearance as the reference procedure. It was shown that the diagnostic capacity of MDRD-eGFR, as it stands, has no added value compared to S-Creatinine. The gender and age differences of the S-Creatinine concentrations in the dataset persist after applying the MDRD-eGFR algorithm. Thus, a general use of the MDRD-eGFR does not seem justified. Furthermore the claim that the eGFR is adjusted for body area is misleading; the algorithm does not include any body size marker. It is thus a dangerous marker for guiding drug administration.

The Modification of Diet in Renal Disease Study equation-estimated glomerular filtration rate (MDRD-eGFR) as a marker for chronic kidney disease, with a single decision level for both genders and all adult ages, requires that the calculated quantity is independent of gender and age. In a retrospective study of S-Creatinine concentrations from laboratory information systems of hospitals in the UK and Sweden, comprising about 140,000 results in total, it was found that the MDRD-eGFR indeed differs between genders and that it varies with age more than the S-Creatinine concentration does. If the age compensation is deleted from the algorithm, the relative changes in the MDRD-eGFR decrease and become almost the same as those for S-Creatinine concentrations. The difference between the genders could probably be overcome by increasing the "if female factor". We used Pt-Iohexol and S-Creatinine concentrations measured simultaneously to estimate the performance of the MDRD-eGFR in relation to Pt-Iohexol clearance. The Pt-Iohexol varies considerably between patients with the same S-Creatinine concentrations, a difference that is not reflected in the MDRD-eGFR. It is concluded that the mathematical transformation of S-Creatinine concentrations does not add any diagnostic value. On the contrary, an increased measurement uncertainty is unavoidable with the use of factors and exponents. The uncertainty is greater than any difference between age and gender in adjacent age groups. There is no compensation for the individual relation between S-Creatinine and Iohexol clearance, and the equation does not consider the individual body surface area; it is therefore inadvisable to use the MDRD-eGFR values as the basis for administration of drugs excreted by the kidneys.

The performance of all measurement procedures used in routine clinical laboratories shall be verified; a minimum is to verify the precision and trueness of the results. This is well established and adequate recommendations and procedures are available. Conveying this information in a form that is adequate and understandable for the practical end-user in the health care sector is still a much debated issue. By tradition, since several decades, the “total error” (TE) is presented, a quantity that is the linear sum of an imprecision and bias. Since any combination of the two can yield the same TE it may not be very helpful in finding and correcting a root-cause for an unacceptable value. Also, an acceptable TE may hide an unacceptable level of its constituents. An alternative is the measurement uncertainty (MU), which is recommended by accreditation and standardizing bodies The MU separates the imprecision and bias and expresses an interval around a best estimate within which the true value is expected with a certain probability. We describe the reporting the best estimate of a measurement result and describe how the uncertainty of the result, can be calculated, using simple custom-made software.

Introduction Ionized calcium (iCa) concentration is often used in critical care and measured using blood gas analyzers at the point of care. Controlling and adjusting regional citrate anticoagulation (RCA) for continuous renal replacement therapy (CRRT) involves measuring the iCa concentration in two samples: systemic with physiological iCa concentrations and post filter samples with very low iCa concentrations. However, modern blood gas analyzers are optimized for physiological iCa concentrations which might make them less suitable for measuring low iCa in blood with a high concentration of citrate. We present results of iCa measurements from six different blood gas analyzers and the impact on clinical decisions based on the recommendations of the dialysis’ device manufacturer. Method The iCa concentrations of systemic and post filter samples were measured using six distinct, frequently used blood gas analyzers. We obtained iCa results of 74 systemic and 84 post filter samples from patients undergoing RCA for CRRT at the University Medicine of Greifswald. Results The systemic samples showed concordant results on all analyzers with median iCa concentrations ranging from 1.07 to 1.16 mmol/L. The medians of iCa concentrations for post filter samples ranged from 0.21 to 0.50 mmol/L. Results of >70 % of the post filter samples would lead to major differences in decisions regarding citrate flow depending on the instrument used. Conclusion Measurements of iCa in post filter samples may give misleading information in monitoring the RCA. Recommendations of the dialysis manufacturer need to be revised. Meanwhile, little weight should be given to post filter iCa. Reference methods for low iCa in whole blood containing citrate should be established.

Laboratory medicine is a challenge for the metrologically and terminologically inclined scientist. One main reason is the need for a sound theory that can be applied in a systematic way to cover all aspects of examinations, i.e., those procedures whose results are reported on an ordinal scale and those reported on more primitive scales (e.g., classifications and narratives). Validation of procedures for examinations involving properties on a nominal scale is especially difficult to achieve because it is hard to find gold standards, in the conventional sense, against which to validate and which combine performance characteristics and clinically relevant specificity and sensitivity. We present a systematic, unambiguously defined terminology (the C-NPU coding scheme) for metrologically derived terms for expressing properties, and present some examples of how to attain diagnostic goals. If the analytic process in the laboratory can be subsumed into medical contexts in a systematic way, many pitfalls in reporting results can be avoided.

Objectives To characterize dynamics of changes of serum levels of TGF-β1 and TNF-α in rats with cardiac fibrosis (CF) occurring during chronic renal failure (CRF), and to reveal the character pf correlations of these factors with amounts of cardiac collagen. Design and Methods. CRF was induced by unilateral nephrectomy and by electrocoagulation of 25% of the cortex of remnant kidney. Post-operative checkpoints were 2, 4, and 6 months. Serum TGF-β1 and TNF-α levels were measured by ELISA. Results. CF became pronounced only at 6 months of CRF, while serum TGF-β1 concentrations reached maximum at 4 months, i.e., at the checkpoint preceding the development of CF. Multiple regression showed cardiac collagen to correlate with both serum TGF-β1 levels and time from the onset of CRF. Sensitivity and specificity of TGF-β1 as serum marker of CF were 86% and 75%.

A comparison of the performance, at two concentrations, of the measurement procedures for 23 common components is presented. For each component the within-, pure between- and total variations have been calculated and an imprecision profile indicated. Thus a pragmatic, readily and generally applicable method is advised to describe the performance of laboratories under repeatability and reproducibility conditions. The calculated total variation is compared with the results estimated from the biological variation of the properties. In most cases the within-laboratory variation is better than that given by the reference database, whereas in about half of the procedures the total variation exceeds that of the reference database. The outcome illustrates the transferability problems that multicentre studies and the diagnosis of patients face by measuring samples using a conglomerate of instruments/laboratories that are not aligned. The calculation procedures are detailed in an appendix and the calculation and presentation of the results are made with a custom-made worksheet program.

To the Editor: Duplicate measurements of patient samples are not common in routine clinical chemistry. The performance of measurements is continuously monitored by the internal quality control (IQC),1 which is not designed to find occasional dropouts. Therefore, the frequency of such errors is not usually known. In the present study, we attempted to estimate the error frequency at commonly suggested imprecision targets by evaluating the difference between 2 adjacent repeated measurements. The frequency is expected to be very low, and therefore the study of this problem required a large number of samples. We measured glucose concentration over a 6-month period in samples obtained from an unselected population of hospitalized patients and outpatients. We used 3 Dimension Vista 1500 analyzers connected to StreamLAB (Siemens Healthcare Diagnostics), in accordance with the manufacturer's instructions. To include measured values in our study, we required that glucose assay performance comply with the RiLiBAEK (Richtlinien der Bundesarztekammer) IQC limits (1) over the measuring interval of 1 mg/dL (0.06 mmol/L) to 500 mg/dL (27.75 mmol/L). We measured 21 653 samples twice, with each sample randomly allocated to one of the instruments by the laboratory automation system. The repeat measurement, which …