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Background With the worldwide increase of diabetes mellitus prevalence, ensuring that HbA1c assays are accurate is essential. External quality assessment (EQA) programs enable laboratories to verify that analytical methods perform according to the manufacturers' specifications. However, assessing trueness requires commutable materials, a property that is rarely characterized for EQA materials. Methods The difference in bias approach was used to assess commutability of 26 processed quality control materials for 17 of the most frequently used HbA1c assays. Involved assays included immuno-assays, enzymatic assays, affinity, ion-exchange HPLC boronate affinity HPLC and capillary electrophoresis. The measurements were performed at manufacturers or expert laboratories. Assay trueness was additionally assessed against the IFCC reference measurement procedure using fresh clinical specimens that were distributed to 450 medical laboratories. Results Commutability of processed EQA materials was highly heterogeneous and globally insufficient to rigorously assess the trueness of HbA1c assays. Using fresh clinical specimens, mean bias was -0.13 mmol/mol for low HbA1c (34 mmol/mol), between +1.0 and +1.3 mmol/mol for intermediate HbA1c (49 and 58 mmol/mol) and +1.2 mmol/mol for elevated HbA1c (90 mmol/mol). Conclusions This study demonstrates that due to insufficient commutability, most processed EQA materials are unsuitable to assess trueness of HbA1c assays and agreement between the different assays. These materials can only provide information on comparability of individual laboratory results with its peers and on assay precision. Using fresh whole blood samples, this study additionally shows that most HbA1c assays are fairly accurate and meet the total allowable error quality target of 5 mmol/mol.

Introduction: Haemoglobin A 1c (HbA 1c ) is considered to be the gold standard for the follow-up of glycaemic control in patients with diabetes mellitus and is also a diagnostic tool. Accordingly, reliable and efficient methods must be used for its quantification. Roche Diagnostics have recently adapted the Tina-quant® HbA 1c Third Generation immunoassay on a fully dedicated analyser, the Cobas c513, which allows a high throughput of up to 400 samples per hour. The present article deals with the evaluation of the analytical performances of this system which has been recently introduced to the market., Materials and Methods: Precision, comparison with two ion-exchange high-performance liquid chromatography (HPLC) methods (Variant II and D-100 systems, BioRad Laboratories) using Passing Bablok and Bland-Altman analyses, accuracy and interference of the most frequent haemoglobin (Hb) variants on HbA 1c measurement were evaluated., Results: Precision was high, with coefficients of variation lower than 1.1% (HbA 1c values expressed in National Glycohemoglobin Standardization Program units, 1.7% for values expressed in International Federation of Clinical Chemistry and Laboratory Medicine [IFCC] units). The comparison study showed similar results with the two HPLC systems. The analysis of samples with IFCC-assigned values showed high methodological accuracy. Finally, no interference of bilirubin, triglycerides and common Hb variants (Hb AC, AD, AE, AS) was observed., Conclusions: This evaluation showed that the analytical performance of the Cobas c513 analyser for HbA 1c assay makes it suitable for a routine use in clinical chemistry laboratories., Competing Interests: Potential conflict of interest: None declared.

Introduction: Haemoglobin A 1c (HbA 1c ) is a key analyte for the monitoring of glycemic balance in diabetic patients and is used for diabetes diagnosis in many countries. The potential interference of carbamylated haemoglobin (cHb) and labile glycated haemoglobin (LA 1c ) on HbA 1c assays must remain a matter of vigilance. Such a situation has occurred in our laboratory with a kit replacement on the Bio-Rad Variant™ II testing system, a cation-exchange high performance liquid chromatography (HPLC) system. With this method, LA 1c and cHb coeluted in a same peak which may have different consequences on HbA 1c values., Materials and Methods: The influence of increasing LA 1c and cHb values on HbA 1c results was studied with in vitro glycation and carbamylation of samples. Samples from patients with high and normal blood urea concentrations were assayed by HPLC and immunological assay., Results: We observed that the degree of interference greatly varied depending on the nature of the interfering Hb fractions found under the so-called "LA 1c peak". Thus, we have decided to apply a decision tree using "LA 1c " thresholds depending on: (i) the retention time, (ii) the shape of the peak, (iii) other analytes, like urea. If the peak recognized as "LA 1c " is mainly formed by LA 1c, we consider that there is no interference until 4%. If the peak is mainly formed by cHb, we consider an interference threshold equal to 2%., Conclusions: This situation reminds that cHb and LA 1c remain critical issues in chromatography-based HbA 1c assays and that adapted criteria must be set up for result interpretation., Competing Interests: Potential conflict of interest: None declared.

Objectives: To quantify serum advanced glycation end-products (AGEs) at the onset of type 1 diabetes mellitus and to determine their potential usefulness as retrospective indicators of glycemic balance., Study Design: Carboxymethyllysine (CML) and pentosidine concentrations were determined by liquid chromatography-tandem mass spectrometry in 3 groups of children with type 1 diabetes mellitus: group (Gr) 1, subjects included at disease onset (n = 36); Gr2, subjects with diabetes of 5 years duration (n = 48); Gr3, subjects with diabetes of 10 years duration and in control subjects (n = 33). Hemoglobin A1c (HbA1c) values were recorded over the entire course of treatment for assessing long-term glycemic balance., Results: Serum AGE concentrations were increased in all groups of subjects with diabetes compared with control subjects, but were highest in Gr1 (for CML: 0.155, 0.306, 0.219, and 0.224 mmol/mol Lys in control, Gr1, Gr2, and Gr3 subjects, respectively; for pentosidine: 312, 492, 365, and 403 nmol/mol Lys, respectively). AGE concentrations were closely correlated with HbA1c values (r = 0.78 for CML; r = 0.49 for pentosidine). In Gr2 and Gr3, the overall glycemic balance estimated by average HbA1c values was positively correlated with CML and pentosidine concentrations, especially in the first year of follow-up., Conclusion: Our results indicate that AGE concentrations are elevated in serum at the time of diabetes mellitus diagnosis, suggesting that the deleterious role of AGEs in the development of long-term complications should be taken into account even at the initial stages of the disease. Moreover, in some circumstances, AGEs could serve as surrogate markers of HbA1c for monitoring glycemic control., (Copyright © 2016 Elsevier Inc. All rights reserved.)

Background: Glycated hemoglobin (HbA1c) is widely used for the monitoring of glycemic balance in diabetic patients and has also been proposed as a tool for the diagnostic of diabetes mellitus. Accordingly, HbA1c quantification must be performed using robust, reliable and efficient methods. Here are reported the results of the evaluation of a new high performance liquid chromatography (HPLC) system for HbA1c quantification, the D-100TM system from Bio-Rad Laboratories., Methods: The analytical performances of the method as well as the influence of the most frequent interferences regarding HbA1c assays (e.g., labile HbA1c, carbamylated hemoglobin, high HbF) have been tested., Results: Intra- and between-assay CVs were respectively lower than 0.93% and 1.46% (HbA1c results expressed in NGSP units) and lower than 1.67% and 2.27% (HbA1c results expressed in IFCC units). The linearity proved to be excellent from 15 mmol/mol (3.5%) to 184 mmol/mol (19.0%) (r=0.999). The results were well correlated with those obtained by another HPLC method (VARIANTTM II Hemoglobin A1c Program reorder pack 270-2101NU-Bio-Rad): HbA1c[VARIANTTM II, mmol/mol]=1.013×HbA1c[D-100TM, mmol/mol]+0.637 (r=0.993, n=2000). The D-100TM system provided results consistent with IFCC-assigned external quality control samples and the presence of labile HbA1c, carbamylated hemoglobin and HbF did not interfere with HbA1c measurement., Conclusions: The D-100 TM system proved to be a robust and reliable method for HbA1c measurement suitable for routine practice in clinical chemistry laboratories.

Background: HbA1c is considered the gold standard for the follow-up of diabetic patients and a new diagnostic tool for diabetes mellitus, which implies the availability of reliable assay methods. We have evaluated a new assay developed by Abbott Laboratories, based on the enzymatic quantification of HbA1c by a fructosyl dipeptide oxidase using Architect analyzers., Methods: Precision, linearity, correlation with a HPLC method, accuracy and potential impact interferences on HbA1c measurement have been evaluated., Results: Intra-day and between-day CVs were lower than 1.2% and linearity was excellent from 19 mmol/mol (3.9%) to 163 mmol/mol (17.1%). The results were well correlated with those obtained by the HPLC (Variant II device, kit NU - BioRad): HbA1c [Architect, mmol/mol]=0.986×HbA1c [Variant II, mmol/mol]+0.713 (r=0.998, n=109). This method provided consistent results with IFCC titrated quality control samples. Classical interferences in HbA1c assays (i.e. labile HbA1c, carbamylated hemoglobin, triglycerides or bilirubin) did not have an impact on HbA1c quantification by this method., Conclusion: This new enzymatic assay proved to be a robust and reliable method for HbA1c measurement suitable for routine practice in clinical chemistry laboratories., (Copyright © 2014 Elsevier B.V. All rights reserved.)

Aim: Assaying HbA1c in patients with haemoglobin variants has long been a technical challenge, despite methodological advances that have progressively limited the problem. The purpose of this study was to evaluate the impact of the most frequent haemoglobin variants on three routine separation methods compared with the IFCC reference method., Patients: Blood samples from heterozygous patients (AS, AC, AD, AE) were analyzed using the IFCC reference method (LC-MS), and the results compared with those obtained by capillary electrophoresis (CAPILLARYS 2 Flex Piercing, Sebia) and two HPLC methods using cation-exchange (Variant II, Bio-Rad) and affinity chromatography (Ultra(2), Primus)., Results: HbA1c values obtained by the IFCC reference method were comparable to those obtained by the three tested methods whatever the haemoglobin variant. Mean relative biases did not exceed the threshold of 7% (above which differences are generally considered clinically significant), although some individual values were above this limit with Variant II in samples with HbS and for all three methods in samples with HbE., Conclusion: This comparative study of the LC-MS reference method and three field methods has demonstrated that these assays are not clinically influenced by the presence of the most common haemoglobin variants. The present results also confirm that the interpretation of HbA1c values in patients with Hb variants remains complex and depends on the assays used and should, in some cases, take into account parameters other than analytical ones (such as differences in glycation rates and half-lives of haemoglobin variants)., (Copyright © 2013 Elsevier Masson SAS. All rights reserved.)

Background: HbA1c is a key biomarker for the monitoring of glycemic balance in diabetic patients. It may be measured by various methods, including HPLC and immunoassays. Here we report the results of the first evaluation of Capillarys 2 Flex Piercing®, a new analyzer using capillary electrophoresis for the separation and the quantification of HbA1c., Methods: We have evaluated the analytical performances of the method as well as the influence of the most frequent analytical interferences regarding HbA1c assays (i.e., labile HbA1c, carbamylated hemoglobin, high HbF and hemoglobin variants)., Results: Intra-assay and between-assays CVs were respectively lower than 1.98% and 2.68% on the pre-market version of the instrument, and lower than 1.62% and 1.45% on the commercial version. The linearity was excellent for HbA1c values ranging from 19 mmol/mol (3.9%) to 161 mmol/mol (16.9%) (r=0.999). The results were well correlated with those obtained by the HPLC method routinely used in the laboratory (Variant II® NU Kit - Bio-Rad): HbA1c[Capillarys 2]=0.9452×HbA1c[Variant II]+1.7279 (r=0.994, n=500). The use of titrated quality control samples indicated a good accuracy of the method. Neither the presence of HbF (until 15%), labile HbA1c or carbamylated hemoglobin, nor that of some typical hemoglobin variants, such as hemoglobin S, D, C and E, affected HbA1c measurement., Conclusions: This evaluation showed that the analytical performances of Capillarys 2 Flex Piercing® analyzer for HbA1c assay fulfilled quality criteria requested for clinical use, and allowed to recommend its implementation in clinical chemistry laboratories for routine practice.

The evaluation of glycated hemoglobin (HbA(1c)) is used in daily practice for monitoring the diabetes mellitus. HbA(1c) may be assayed by different methods, among which high-pressure liquid chromatography (HPLC). We have evaluated a new kit 2.0 available on HPLC Variant II(®) Turbo analyzer (Bio-Rad), which is characterized by an elution buffer containing sodium perchlorate. The correlation with the routine method used in our laboratory (HPLC Variant II(®) analyzer equipped with the NU kit) is good (r² = 0.997). Intra- and inter-assay coefficients of variation are respectively lower than 0.6 and 1.6%. Linearity is excellent from 3.2% (11 mmol/mol) to 18.3% (177  mmol/mol). There is no inter-sample contamination. This method provides a result quickly (96  seconds), but does not allow separating labile HbA(1c) from carbamylated hemoglobin, contrary to the NU kit. As the control of analytical quality is a major concern for validation and clinical use of HbA(1c) results, the characteristics of this new kit make it a well-suited tool for daily laboratory practice.

HbA(1c) represents a key parameter in the monitoring of glycemic balance in diabetic patients. It may be assayed by various methods, among which high-pressure liquid chromatography (HPLC). We have evaluated a new HPLC analyzer, Glycomat 3000 (Biocode Hycel). HbA(1c) values are well correlated (r(2) = 0.994) with those obtained by the HPLC analyzer used routinely in our laboratory (Variant II, Bio-Rad). However, the precision of assays can be at the limit of acceptability (CV of repeatability between 0.7 and 1.4% and CV of reproducibility between 3.3 and 4.1%) if strict conditions of calibration and quality control are not implemented. The assay is sensitive to the interference of modified fractions of hemoglobin (labile HbA(1c) and carbamylated Hb) in the clinical range, and to the presence of HbF. Besides, Glycomat 3000 is a friendly and easy to use analyzer.

HbA(1c) assay by high-pressure liquid chromatography (HPLC) remains submitted to various analytical interferences. We have evaluated the behaviour of the analyzers G8 (Tosoh Bioscience) and Variant II (BioRad) towards the most common interferences (i.e. labile fraction of HbA(1c), carbamylated hemoglobin, bilirubin, triglycerides, hemoglobin variants). This comparative study showed that the influence of these interferences varied according to the analyzer and depended on various settings such as the chromatographic resolution and the peak integration mode. However, this influence remains limited when strict and analyzer-specific rules of technical validation have been previously determined. The outcome of the study underlines the importance of a detailed interpretation of chromatograms during the biological validation process, and recommends specific procedures in case of interferences, in order to ensure the reliability of HbA(1c) results.

The methods of HbA1c assay using ion exchange high pressure liquid chromatography (HPLC) allow the detection of the most common hemoglobin variants. This observation highlights the different behaviour of two HPLC analyzers in the presence of Tatras hemoglobin. By one of the analyzer (Variant II, Bio-Rad) this variant is detected, but not by the other (G8, Tosoh Biosciences). As HbA1c result is crucial for the therapeutic decision, it is important that biologists know the characteristics of the method they use, in order to detect the possible occurence of an hemoglobinopathy and to ensure the best interpretation of the result.