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Icterus, a phenomenon caused by bilirubin elevation in the blood, is a common endogenous interference in chemistry testing, occurring either spectrally or through chemical reactivity with assay reagents. Often, laboratories have few options other than to dilute or reject samples exceeding icteric thresholds. However, recent studies have optimized in vitro photoisomerization of bilirubin to a 17-minute bilirubin half-life using 500 nm light at 37 °C. Using an enzymatic creatinine assay as a model, due to its prevalence in routine laboratory testing and susceptibility to icteric interference, our study explores the usage of in vitro photoisomerization by replicating these conditions in a device, the Bilibox, as means of resolving icterus in laboratory testing. Left-over icteric and non-icteric clinical samples, collected by lithium heparin vacutainer (n = 10), were analyzed for baseline creatinine, diluted creatinine (1:4 0.9 % NaCl), total bilirubin, direct bilirubin, and hemolysis, icterus and lipemia (HIL) indices. Samples were then placed in the Bilibox in two intervals of 30 min with repeat measurements of the aforementioned analytes. On average, icteric-index, total bilirubin (TBIL), and direct bilirubin (DBIL) decreased by 33.5, 39.1 and 39.9 % respectively following 30 min of Bilibox treatment; and by 47.6 %, 63.7 % and 59.8 % following 60 min. The average percent difference between the pre-exposure diluted and undiluted creatinine was 5.8 %, demonstrating the icterus interference. Following Bilibox treatment, the difference between undiluted (post-exposure) and diluted (pre-exposure) creatinine decreased to 0.02 % (p = 0.0232) and 2.2 % (p = 0.0021) at 30 and 60 min of treatment respectively, demonstrating resolution of interference. Consequently, photoisomerization can be utilized as an additional and reasonably quick method for resolving icterus when dilutional methods cannot be applied.

In 2017, the American College of Gastroenterology (ACG) and the North American Society of Pediatric Gastroenterology, Hepatology and Nutrition published clinical guidelines recommending the use of alanine aminotransferase (ALT) upper reference limits (URL) of 33, 25, 26, and 22 U/l for men, women, boys, and girls, respectively. This was opposed by laboratory experts who advocated for the use of higher URL of 59, 41, 33, and 24 U/l instead. We suspected that the variable inclusion of individuals who consumed alcohol to be a major contributing source of URL variability and debate.Outpatient ALT data (n = 7379) were collected from unique individuals ≥13 y with BMIs of ≥19 and ≤25. A total of 222 (3%) were excluded due to suspected liver disease. Patients were split into a pediatric group (age 13-17 y), an alcohol-restricted adult group (age 18-20 y), and adults with access to alcohol by decade (i.e., age 21-29, 30-39, 40-49, 50-59, 60-69, 70-79, and ≥ 80 y). All ALT values were measured on Roche Cobas 8000 with pyridoxal phosphate and traceable to the IFCC-reference measurement procedure.We derived URL similar to CALIPER for our pediatric population, but closer to ACG-proposed URL in our alcohol-restricted adult group. The URL increased significantly in men and women for all other age groups.The discrepancy in ALT URL in clinical laboratories may be attributable in part due to the variable inclusion of individuals who recently consumed alcohol in local population derivation studies.

Aggrecan is a large proteoglycan that forms giant hydrated aggregates with hyaluronan in the extracellular matrix (ECM). The extraordinary resistance of these aggregates to compression explains their abundance in articular cartilage of joints where they ensure adequate load-bearing. In the brain, they provide mechanical buffering and contribute to formation of perineuronal nets, which regulate synaptic plasticity. Aggrecan is also present in cardiac jelly, developing heart valves, and blood vessels during cardiovascular development. Whereas aggrecan is essential for skeletal development, its function in the developing cardiovascular system remains to be fully elucidated. An excess of aggrecan was demonstrated in cardiovascular tissues in aortic aneurysms, atherosclerosis, vascular re-stenosis after injury, and varicose veins. It is a product of vascular smooth muscle and is likely to be an important component of pericellular matrix, where its levels are regulated by proteases. Aggrecan can contribute to specific biophysical and regulatory properties of cardiovascular ECM via the diverse interactions of its domains, and its accumulation is likely to have a significant role in developmental and disease pathways. Here, the established biological functions of aggrecan, its cardiovascular associations, and potential roles in cardiovascular development and disease are discussed.

AimsPneumatic tube systems (PTSs) are critical for modern hospital operations, allowing for rapid sample transport. Despite widespread use, PTSs can compromise specimen integrity and affect laboratory values. Our objective was to prove that rapid serum clot tubes (RST) provide protective benefits over plasma during PTS transport and can be a practical solution for certain PTS routes.MethodsIn this study, we compared the effects of PTS transport on cell lysis indicators: h-index, lactate dehydrogenase (LDH) and potassium (K+), in RST versus lithium heparin gel separator tubes using 10 volunteers.ResultsIn comparison with plasma, RST showed a median reduction in PTS-induced haemolysis of 80.4% (p=0.0049), with a reduction in post-PTS median LDH concentration (49.7%, p=0.04) and K+ concentration (50.0%, p=0.0273).ConclusionThis study demonstrates RST tubes can significantly reduce PTS-induced haemolysis and can be recommended for poor PTS routes.

Background Heart-type fatty acid binding protein (H-FABP), a low molecular weight protein found primarily in myocardial tissue, has been identified as a potential biomarker in the detection of acute coronary syndrome and acute kidney injury. To further investigate clinical utility, we sought to establish an upper reference limit (URL) of H-FABP within a healthy U.S. population. Methods Serum samples of healthy donors were acquired from the AACC Universal Sample Bank. We analyzed 355 samples for H-FABP concentration using the Randox Laboratories immunoturbidimetric assay on the Roche Cobas 8000 series analyzer. Results The final sample population consisted of individuals aged 18–74 y, with 170 males and 185 females. The distribution of the population exhibited a strong positive skew, affecting outlier analysis and URL determination. The 97.5th-percentile URL was found to be 7.4 ng/ml (95% CI: 6.3–9.2), while the 99th-percentile URL was 12.1 ng/ml (8.6–14.9). Conclusion As the URL for H-FABP is highly affected by population distribution and outlier removal, final determination for an assay cutoff should be made in the context of clinical utility, either as a standalone assay or in conjunction with other biomarkers, and the desired clinical sensitivity and specificity.

Background Pseudohyponatremia describes an artifactual decrease in plasma sodium result in samples with high proteins and/or lipids when measured by an indirect ion-selective electrode (ISE) method. We suspected that Intralipid®-based lipemia cutoffs are inappropriate for detecting interfering lipids in human samples and a major contributing factor to the existence of pseudohyponatremia. Methods We evaluated 2 approaches to derive a lipemia cutoff for sodium, one in which patient plasma samples were pooled and spiked to simulate hyperlipidemia using Intralipid® (commonly used approach by in-vitro diagnostics manufacturers), and another in which endogenous hyperlipidemic samples (n = 31) were measured by methods not affected by hyperlipidemia (i.e., direct ISE and post-ultracentrifugation indirect ISE). Triglycerides, lipemic index (L-index) and indirect ISE sodium concentrations of samples were measured on Roche Cobas® 8000 and direct ISE on Radiometer® ABL835 Flex analyzers. Endogenous hyperlipidemic samples were also ultracentrifuged on Beckman Coulter® Airfuge to clear excess lipids and re-analyzed for sodium by indirect ISE. Results We discovered that Intralipid® is not an accurate emulation of the lipemic interference seen in pseudohyponatremia because it showed no effect up to the maximum level of lipemia tested (L-index = 2000). By contrast, endogenous hyperlipidemic samples demonstrated significant deviations in sodium concentration (≥4 mmol/l) when L-index approached or exceeded 700, and a strong positive correlation between L-index and the difference between the indirect and direct methods (i.e., extent of pseudohyponatremia). Conclusions Clinical laboratories should lower their tolerance for lipemia from the currently recommended L-index cutoff of 2000 on Roche Cobas 8000®. We recommend reflexing to direct ISE when L-index exceeds 700. Manufacturers and laboratories with other indirect ISE methods should evaluate the effect of lipid interference on their method using hyperlipidemic human samples not Intralipid®.

Background Dronabinol is used to treat a variety of conditions, including loss of appetite in people with AIDS and severe nausea and vomiting caused by cancer chemotherapy. Its therapeutic potential for pain management is now being explored in specific populations. Monitoring dronabinol compliance is challenging because its active ingredient, Δ-9-tetrahydrocannabinol (THC), is also present in cannabis. We developed a rapid LC-MS/MS assay with minimal specimen preparation to quantitate 11 cannabinoids in urine. Using this assay coupled with urine samples from normal controls, cannabis, and dronabinol users, we show the ability to differentiate cannabis from dronabinol use. Methods Residual clinical urine samples from 55 cannabinoid positive subjects and 31 negative controls, as well as prospective samples from 5 patients receiving dronabinol therapy were obtained for analysis. Results In the dronabinol group, only the THC metabolites 11-nor-9-carboxy-tetrahydrocannabinol (THC-COOH) and 11-hydroxy-Δ-9-tetrahydrocannabinol (THC-OH) were detected. Minor cannabinoids were detected in 91% of cannabis group samples and their detection was more frequent in samples with increased THC metabolite concentrations. Of minor cannabinoids evaluated, cannabigerol (CBG) and cannabidiol (CBD) had the greatest sensitivity in detecting cannabis use. Conclusions This method has a high sensitivity for the detection of cannabis use with implications for evaluating dronabinol compliance.

As composites of a core protein and several chemically distinct types of glycosaminoglycan (GAG) chains, proteoglycans are diverse molecules that occupy a unique niche in biology. They have varied and essential roles as structural and regulatory molecules in numerous physiological processes and disease pathology. In regard to cellular context, some link the interior of the cell to the extracellular matrix (ECM) as transmembrane or membrane-anchored molecules with a major role in cell adhesion and signal transduction. Others reside in pericellular matrix, where they influence crucial aspects of cell behavior, and several reside in interstitial ECM as components of structural macromolecular networks. Because of their unique composition, they can be challenging to identify and characterize using conventional biochemical or antibody-based methods. In contrast, the GAG component, despite its immense chemical diversity, typically carries a strong net negative charge which can be exploited to advantage for affinity-isolation and enrichment of proteoglycans from any biological system in a core protein-, GAG-, tissue-, and species-agnostic manner by anion exchange chromatography. This method, when coupled with high resolution liquid-chromatography tandem mass spectrometry (LC-MS/MS) can be used to define the proteoglycanome of any cell type, tissue or organism. A proteoglycanomics strategy can be further refined by inclusion of additional orthogonal affinity steps or fractionation for greater specificity and to deliver proteoglycans with distinct specified characteristics. Moreover, elimination of the GAG chain chemically and/or obliteration of the core protein enables glycomics characterization of GAG structure. Enzymatic digestion of GAGs on tryptic peptides allows mapping of glycopeptides, which has been used for identification of novel proteoglycans and to precisely define sites of GAG attachment. Recent application of proteoglycanomics to human aorta and human aortic aneurysms demonstrated its potential to identify tissue and disease proteoglycanomes and the detailed method that was used is provided here for application to other tissues or biological systems.

Context Leiomyomas have abundant extracellular matrix (ECM), with upregulation of versican, a large proteoglycan. Objective We investigated ADAMTS (a disintegrin-like and metalloprotease with thrombospondin type 1 motifs) protease-mediated versican cleavage in myometrium and leiomyoma and the effect of versican knockdown in leiomyoma cells. Design We used quantitative reverse transcription polymerase chain reaction (qRT-PCR), western blotting, immunohistochemistry, and RNA in situ hybridization for analysis of myometrium, leiomyoma and immortalized myometrium and leiomyoma cells. Short interfering RNA (siRNA) was used to knockdown versican in leiomyoma cells. Setting This study was performed in an academic laboratory. Patients Study subjects were women with symptomatic or asymptomatic leiomyoma. Main Outcome Measures We quantified messenger RNAs (mRNAs) for versican splice variants. We identified ADAMTS-cleaved versican in myometrium and leiomyoma and ADAMTS messenger RNAs and examined the effect of VCAN siRNA on smooth muscle differentiation and expression of estrogen and progesterone receptors. Results The women in the symptomatic group (n = 7) had larger leiomyoma (P = 0.01), heavy menstrual bleeding (P < 0.01), and lower hemoglobin levels (P = 0.02) compared with the asymptomatic group (n = 7), but were similar in age and menopausal status. Versican V0 and V1 isoforms were upregulated in the leiomyomas of symptomatic versus asymptomatic women (P = 0.03 and P = 0.04, respectively). Abundant cleaved versican was detected in leiomyoma and myometrium, as well as in myometrial and leiomyoma cell lines. ADAMTS4 (P = 0.03) and ADAMTS15 (P = 0.04) were upregulated in symptomatic leiomyomas. VCAN siRNA did not effect cell proliferation, apoptosis, or smooth muscle markers, but reduced ESR1 and PR-A expression (P = 0.001 and P = 0.002, respectively). Conclusions Versican in myometrium, leiomyomas and in the corresponding immortalized cells is cleaved by ADAMTS proteases. VCAN siRNA suppresses production of estrogen receptor 1 and progesterone receptor-A. These findings have implications for leiomyoma growth.

ADAMTS (A Disintegrin-like and Metalloproteinase domain with Thrombospondin type 1 Motif)-1, -4 and -5 share the abilities to cleave large aggregating proteoglycans including versican and aggrecan. These activities are highly relevant to cardiovascular disease and osteoarthritis and during development. Here, using purified recombinant ADAMTS-1, -4 and -5, we quantify, compare, and define the molecular basis of their versicanase activity. A novel sandwich-ELISA detecting the major versican cleavage fragment was used to determine, for the first time, kinetic constants for versican proteolysis. ADAMTS-5 (kcat/Km 35 × 105 M−1 s−1) is a more potent (~18-fold) versicanase than ADAMTS-4 (kcat/Km 1.86 × 105 M−1 sec−1), whereas ADAMTS-1 versicanase activity is comparatively low. Deletion of the spacer domain reduced versicanase activity of ADAMTS-5 19-fold and that of ADAMTS-4 167-fold. Co-deletion of the ADAMTS-5 cysteine-rich domain further reduced versicanase activity to a total 153-fold reduction. Substitution of two hypervariable loops in the spacer domain of ADAMTS-5 (residues 739–744 and 837–844) and ADAMTS-4 (residues 717–724 and 788–795) with those of ADAMTS-13, which does not cleave proteoglycans, caused spacer-dependent reductions in versicanase activities. Our results demonstrate that these loops contain exosites critical for interaction with and processing of versican. The hypervariable loops of ADAMTS-5 are shown to be important also for its aggrecanase activity. Together with previous work on ADAMTS-13 our results suggest that the spacer domain hypervariable loops may exercise significant control of ADAMTS proteolytic activity as a general principle. Identification of specific exosites also provides targets for selective inhibitors.

Highlights • • A novel Vcan mouse allele, VcanAA, has ADAMTS protease-resistant versican. • • VcanAA/AA mice are viable and develop soft tissue-syndactyly (STS) • • VcanAA/AA STS is rendered more severe in combination with Adamts20Bt/Bt. • • Mice lacking the versican GAGβ domain, but not the GAGα domain, also have STS. • • The versican GAGβ proteolytic fragment versikine is necessary for web regression., Two inherent challenges in the mechanistic interpretation of protease-deficient phenotypes are defining the specific substrate cleavages whose reduction generates the phenotypes and determining whether the phenotypes result from loss of substrate function, substrate accumulation, or loss of a function(s) embodied in the substrate fragments. Hence, recapitulation of a protease-deficient phenotype by a cleavage-resistant substrate would stringently validate the importance of a proteolytic event and clarify the underlying mechanisms. Versican is a large proteoglycan required for development of the circulatory system and proper limb development, and is cleaved by ADAMTS proteases at the Glu441-Ala442 peptide bond located in its alternatively spliced GAGβ domain. Specific ADAMTS protease mutants have impaired interdigit web regression leading to soft tissue syndactyly that is associated with reduced versican proteolysis. Versikine, the N-terminal proteolytic fragment generated by this cleavage, restores interdigit apoptosis in ADAMTS mutant webs. Here, we report a new mouse transgene, VcanAA, with validated mutations in the GAGβ domain that specifically abolish this proteolytic event. VcanAA/AA mice have partially penetrant hindlimb soft tissue syndactyly. However, Adamts20 inactivation in VcanAA/AA mice leads to fully penetrant, more severe syndactyly affecting all limbs, suggesting that ADAMTS20 cleavage of versican at other sites or of other substrates is an additional requirement for web regression. Indeed, immunostaining with a neoepitope antibody against a cleavage site in the versican GAGα domain demonstrated reduced staining in the absence of ADAMTS20. Significantly, mice with deletion of Vcan exon 8, encoding the GAGβ domain, consistently developed soft tissue syndactyly, whereas mice unable to include exon 7, encoding the GAGα domain in Vcan transcripts, consistently had fully separated digits. These findings suggest that versican is cleaved within each GAG-bearing domain during web regression, and affirms that proteolysis in the GAGβ domain, via generation of versikine, has an essential role in interdigital web regression.

We compared two different methods of whole blood sodium measurement to plasma sodium measurement using samples in the profoundly hyponatremic range (Na120 mmol/L).Whole blood pools with a range of low sodium values were generated using combinations and dilutions of pooled electrolyte-balanced lithium heparin samples submitted for arterial blood gas analysis. Each pool was analyzed five times on a Radiometer 827 blood gas analyzer and iSTAT analyzer. Pools were centrifuged to produce plasma, which was analyzed five times on a Roche Cobas c501 chemistry analyzer. An additional 40 fresh (analyzed on day of collection) excess lithium heparin arterial blood gas samples from 36 patients were analyzed on the Radiometer 827, iSTAT, and Cobas c501 as described above. The setting was a tertiary referral center. Blood samples were collected from a combination of patients in the intensive care unit, operating theaters and emergency room.All methods demonstrated excellent precision, even in the profoundly hyponatremic measurement range (Na120 mmol/L using a plasma reference method). However, agreement between the methods varied with the degree of hyponatremia. In the profoundly hyponatremic range, Radiometer whole blood sodium values were nearly identical to plasma reference sodium, while iSTAT whole blood sodium showed a consistent positive bias relative to plasma sodium in this range.If whole blood direct sodium measurements are compared with plasma sodium in profoundly hyponatremic patients consideration should be given to the use of Radiometer blood gas analyzers over iSTAT since the latter shows a positive bias relative to a plasma comparative method.

Warfarin dosing relies on accurate measurements of international normalized ratio (INR), which is calculated from the prothrombin time (PT), International Sensitivity Index international sensitivity index (ISI) of the thromboplastin, and the geometric mean of normal PT (MNPT). However, ISI assignments of certain reagent/instrument combinations are frequently unavailable, especially when the reagent and instrument are not from the same manufacturer. The effort to be in compliance with widely endorsed Clinical and Laboratory Standards Institute (CLSI) guidelines by locally verifying or assigning an ISI to an unsupported reagent/instrument combination is further hindered by the lack of US Food and Drug Administration (FDA)-approved certified plasmas designated for a particular reagent/instrument combination. The objectives of the study include development of a process to verify/assign ISI and MNPT of a single thromboplastin reagent from one manufacturer across multiple instruments including several from another manufacturer and across several campuses of a single institution, the Mayo Clinic. In this study, RecombiPlasTin 2G (R2G), was evaluated on the ACL TOP 700 (IL), STA-R Evolution, STA Compact, and STA Satellite. Random normal donor samples (n = 25) were used to verify/assign MNPT. A subset of the normal donors (n = 8) and 13 warfarin pools (INR range: 1.3-3.9), created from stable warfarin patient plasma, were used for ISI verification/assignment. The manufacturer's assigned ISI was first verified on the ACL TOP 700 (reference method), then assigned on three unsupported instruments using orthogonal regression analysis. The MNPT and manufacturer assigned ISI (11.0, 0.95) were verified on the ACL TOP 700 and subsequently assigned on the STA-R Evolution (11.6, 1.04); STA Compact (11.5, 1.02); and STA Satellite (10.9, 0.99). Linear correlations of the INR results from all the four instruments demonstrated an r2 > 0.99. This process provides a reproducible approach to assigning ISIs on unsupported reagent/instrument combinations. Our data also confirm that ISIs of the same PT reagent differ significantly on different instruments, thus confirming the requirement for evaluations and validation of ISIs for different reagent/instrument combinations.

Objectives Point of care (POC) whole blood lactate testing may facilitate rapid detection of sepsis. We evaluated three POC methods against both plasma lactate comparison methods and a flow-injection mass spectrometric (MS) method. Design and Methods Nova StatStrip, Abbott i-STAT CG4 + and Radiometer ABL90 POC lactate methods were evaluated against the mean of Cobas Integra 400 and Vitros 350 plasma lactate. POC methods were also compared to a flow-injection mass spectrometric assay measuring lactate in ZnSO4-precipitated whole blood extracts. Intra- and inter-assay precision was determined using quality control material. Method comparison included specimens from normal donors at rest, after exertion, and after spiking with lactic acid. Results Intra- and inter-assay coefficient of variation was 6 mmol/L, all POC methods showed proportional negative bias compared to plasma methods; but this bias was not observed when compared to the MS method. Despite proportional negative bias, all POC methods demonstrated acceptable concordance (94–100%) with plasma lactate within the reference interval ( 4 mmol/L, commonly used clinical cut-offs for detection of sepsis. Conclusions POC lactate methods demonstrate acceptable concordance with plasma lactate across commonly used clinical cut-offs for detection of sepsis. Due to systematic negative bias at higher lactate concentrations, POC and plasma lactate should not be used interchangeably to monitor patients with elevated lactate concentrations.

Previous studies have found positive bias and frequent outliers when central venous catheter (CVC) whole blood is used to dose glucose meters. We designed a study to determine whether positive bias and outliers with CVC whole blood glucose samples are due to exogenous glucose contamination of CVC samples, inherent bias and imprecision of glucose meters, or properties of CVC whole blood that interfere with the function of some glucose meters.We studied the relationship between venous whole blood and venous plasma glucose drawn by venipuncture to CVC whole blood and CVC plasma glucose in 50 hospitalized patients. In 27 patients whole blood glucose was measured on both the Accu-Chek Inform (Roche Diagnostics, Indianapolis, IN) and StatStrip (Nova Biomedical, Waltham, MA).By comparing CVC plasma to venous plasma glucose, we determined that contamination of CVC samples with exogenous glucose was uncommon. On the Inform meter outliers were approximately twice as common with CVC whole blood compared to venous whole blood. In 27 patients who had CVC whole blood analyzed by both Inform and StatStrip, outliers occurred approximately twice as often on the Inform compared to the StatStrip. Accounting for CVC samples contaminated with exogenous glucose, outliers on the StatStrip did not occur significantly more often using CVC whole blood compared to venous whole blood.Properties unique to CVC whole blood differentially affect glucose meter bias and imprecision. Device selection is critical in practices that wish to use CVC whole blood to monitor glucose concentration in hospitalized patients.

Objectives After several hemolyzed blood samples were received in the laboratory, we investigated lipid emulsion/TPN as a novel cause of hemolysis. Design and methods Whole blood was spiked with lipid emulsion and TPN. Results Hemolysis was proportional to the amount of lipid emulsion present in whole blood, with less hemolysis occurring in blood gas syringes compared to vacutainer tubes. Conclusion Collection of specimens in blood gas syringes may prevent hemolysis in patients on lipid emulsion.

The performance of three point of care methods for pleural fluid pH analysis was compared to a currently validated blood gas analyzer.An ABL 725 (Radiometer America, Westlake, OH) was used as the reference method to evaluate three cartridge-based assays: ABL 90 FLEX (Radiometer), and i-STAT 1 (Abbott Point of Care, Abbott Park, IL) CG4+ and G3+ cartridges for pleural fluid pH analysis. Pooled residual pleural fluid samples and quality control material were analyzed to determine intra- and inter-assay precision. Method comparison was performed with spiked (n=40) and clinically-ordered (n=10) pleural fluid samples across the analytical measuring range.All methods demonstrated inter-assay CVs0.1% at pH values of 7.1 and 7.6, and intra-assay CVs0.3% at pH values of 7.2 and 7.7. Bland-Altman plots demonstrated clinically significant bias between ABL 725 and each cartridge-based method only at pH7.6. For samples with pH7.6 mean bias vs. ABL 725 was -0.01 for ABL 90 FLEX and 0.03 for i-STAT 1 CG4+ and G3+ cartridges. Clinical concordance using a decision limit of pH7.2 was 96-98% for the three methods.Analytical and clinical performance of the three cartridge-based methods was comparable to a validated blood gas analyzer for pleural fluid pH analysis. Cartridge-based pH methods offer the advantage of easier troubleshooting for clots and clogs as they use disposable electrodes. However cartridge-based methods are not currently FDA-approved for pleural fluid samples, such that additional validation would be required for this specimen type.

Objectives To minimize toxicity of high-dose methotrexate (MTX) therapy, urinary alkalinization with frequent monitoring of urine pH is required. Urine pH is usually assessed by fast and convenient dipstick methods. When urine color interferes with dipstick measurement, as occurs in patients receiving MTX, alternative methods such as pH meters are used. Nursing staff caring for patients on high-dose MTX reported that urine pH results from dipstick and pH analyzers were often clinically discordant. As a result urine pH by dipstick and pH meter were compared in patients on high-dose MTX therapy and patients with normal-colored urine samples. Design and methods We measured urine pH by dipstick and pH meter in 116 urine samples from 4 patients receiving high-dose MTX therapy, and in 50 normal-colored urine samples from 50 patients not on MTX therapy. Results In patients on MTX therapy the mean (± standard deviation) bias between dipstick and pH meter urine pH was 0.7 ± 0.4, compared to 0.4 ± 0.3 in patients not on MTX. For patients on MTX clinical concordance between dipstick and pH meter urine results was poor around a clinical cut-off of pH 8.0. Of the 92 samples with a meter urine pH ≤ 8.0, 72 had a discordant value by dipstick (pH > 8). Conclusions Urine pH readings by dipstick and pH meter are not equivalent, and the bias between them is exacerbated in patients on MTX. Institutions with high-dose MTX therapy protocols should not alternate between dipstick and pH meter urine pH monitoring.