Recommendations for the implementation of international standardization of glycated hemoglobin in Italy

Defining allowable total error limits in the clinical laboratory

Allowable total error (ATE) are performance specification limits predefined for a variety of laboratory analytes. These limits define the maximum amount of error that is allowed for an assay when judging acceptability of a new assay during method verification/validation, evaluating patient or instrument comparison data, or in designing a quality control strategy. There are several widely available resources and models that can serve as a guide in selecting ATE. They may be based on legal requirements or set by providers of proficiency testing (PT) and external quality assessment schemes (EQAS). ATE can be also determined by professional expert groups or be based on biological variation of an analyte. Because there are several resources to choose from, there have been several attempts in reaching consensus on which ATE resource should be given preference. This chapter reviews several of these resources in more detail and discusses the difference between allowable total error (ATE) and observed total analytical error (TAE).

Analytical performance evaluation of the Norudia HbA1c assay

BACKGROUND

Hemoglobin A1c (HbA1c) is arguably the most important biomarker used in the diagnosis and treatment monitoring of diabetes mellitus. We evaluated the analytical performance of the Norudia HbA1c assay (Sekisui Medical Co., LTD), which uses an enzymatic method incorporated into a fully automated, high-throughput system.

METHODS

The precision, linearity, and carryover of the Norudia HbA1c assay were evaluated. Using 60 patient samples, comparative analysis of HbA1c measurements with two commonly used HbA1c assays, the D100 (Bio-Rad Laboratories, Inc) and HLC-723 G11 (Tosoh), was undergone. Thirteen commutable samples with known HbA1c concentrations measured using an IFCC reference measurement procedure were used to compare accuracy between methods. Interference of HbA1c measurement by Hb variants was evaluated using 16 known Hb variant samples.

RESULTS

Repeatability (% CV) for low and high concentrations ranged from 1.12%-1.50% and 0.66%-0.75%, respectively, and within-laboratory precision for low and high concentrations ranged from 1.73%-2.89% and 0.98%-1.64%, respectively. For linearity, the coefficient of determination was 0.9987. No significant carryover was observed. When compared to the D100 and HLC-723 G11 assays, the Norudia HbA1c assay showed the best accuracy with the lowest mean bias (-1.72%). Furthermore, the Norudia was least affected by Hb variants and gave the most reliable HbA1c measurements.

CONCLUSION

The Norudia HbA1c showed excellent analytical performance with good precision and linearity, and minimal carryover. When compared to other routine HbA1c methods, the Norudia HbA1c assay showed the highest accuracy and was least affected by Hb variants.

The estimation of uncertainty of measurement of glycated hemoglobin as an analytical performance specification and in the interpretation of its results

BACKGROUND

Glycated hemoglobin (HbA1c) plays a key role in monitoring the glycemic state of an individual. Uncertainty of measurement (U) indicates the magnitude of the doubt about a measurement result. To properly classify an individual as under either good or poor glycemic control, it has been suggested that U of an HbA1c result should not exceed ±0.5%.

METHODS

The statistical method used to calculate uncertainty of measurement was the "top down" approach suggested by EURACHEM/CITAC. This approach allows the inclusion of imprecision, bias, uncertainty of bias and uncertainty of the calibration of the HbA1c method. The value of bias was obtained using data generated from the external quality assessment of the Randox International Quality Assessment Scheme and that of the Unity data management software system. Imprecision was calculated after the daily analysis of two levels of control sera.

RESULTS

Calculation of uncertainty of measurement of HbA1c was a straightforward procedure used to calculate U. Due to the different bias results obtained using two different external quality programs, the results of U were significantly different (±0.19% vs ± 0.43%) from each other; however, in both cases, the U results were below the maximal suggested uncertainty of ±0.5%.

CONCLUSIONS

The calculation of U of HbA1c by the EURACHEM/CITAC method is a practical approach that can be used as an additional analytical goal in the measurement of HbA1c. In addition, this information can aid clinicians to determine the level of confidence that can be placed in the test results.

New HPLC instrument performance evaluation in HbA1c determination and comparison with capillary electrophoresis

Glycated hemoglobin (HbA_1c) measurement provides the most important medium to long-term marker of time-averaged glycemic status. Its relationship to clinical outcome in diabetes has been convincingly demonstrated for both type 1 and type 2 diabetes. The main HbA_1c measurement methods for clinical routine are as follows: ion-exchange chromatography; affinity chromatography, capillary electrophoresis, immunoassay and enzymatic methods. In this study, we evaluated the analytical performances of a new HPLC instrument (Tosoh HLC-723 G11 in the VAR mode) in HbA_1c analysis and compared it with a capillary electrophoresis instrument (Sebia Capillarys 2 Flex Piercing). HbA_1c analysis was performed in parallel by both methods for 250 samples randomly chosen from healthy and diabetic subjects at 'Tor Vergata' University Hospital of Rome. Tosoh HLC-723 G11 showed good reproducibility for 10 days both in quality controls and in samples analyzed (%CV < 2%). We found good linearity for HbA1c values ranging from 15 mmol/mol (3.5%) to 178 mmol/mol (18.5%), with a correlation coefficient R² = 1. In a comparison between Tosoh HLC-723 G11 and Capillarys 2FP a good correlation (r = 0.99) was found; however, Tosoh HLC-723 G11 showed higher values in the low range of HbA_1c and lower in the high range (Tosoh HLC-723 G11 = 4.3043 + 0.913 Capillarys 2FP; p < 0.001). Tosoh HLC-723 G11 showed good repeatability, reproducibility, accuracy and automated simplicity, and it seemed suitable for routine use in clinical chemistry laboratories.

Methods, units and quality requirements for the analysis of haemoglobin A1c in diabetes mellitus

The formation of glycohemoglobin, especially the hemoglobin A_1c (HbA_1c) fraction, occurs when glucose becomes coupled with the amino acid valine in the β-chain of Hb; this reaction is dependent on the plasma concentration of glucose. Since the early 1970s it has been known that diabetics display higher values OF HbA_1C because they have elevated blood glucose concentrations. Thus HbA_1c has acquired a very important role in the treatment and diagnosis of diabetes mellitus. After the introduction of the first quantitative measurement OF HbA_1C, numerous methods for glycohemoglobin have been introduced with different assay principles: From a simple mini-column technique to the very accurate automated high-pressure chromatography and lastly to many automated immunochemical or enzymatic assays. In early days, the results of the quality control reports for HbA_1c varied extensively between laboratories, therefore in United States and Canada working groups (WG) of the Diabetes Controls and Complications Trial (DCCT) were set up to standardize the HbA_1c assays against the DCCT/National Glycohemoglobin Standardization Program reference method based on liquid chromatography. In the 1990s, the International Federation of Clinical Chemistry and Laboratory Medicine (IFCC) appointed a new WG to plan a reference preparation and method for the HBA_1c measurement. When the reference procedures were established, in 2004 IFCC recommended that all manufacturers for equipment used in HbA_1c assays should calibrate their methods to their proposals. This led to an improvement in the coefficient of variation (CV%) associated with the assay. In this review, we describe the glycation of Hb, methods, standardization of the HbA_1c assays, analytical problems, problems with the units in which HbA_1c values are expressed, reference values, quality control aspects, target requirements for HbA_1c, and the relationship of the plasma glucose values to HbA_1c concentrations. We also note that the acceptance of the mmol/mol system for HbA_1c as recommended by IFCC, i.e., the new unit and reference ranges, are becoming only slowly accepted outside of Europe where it seems that expressing HbA_1c values either only in per cent units or with parallel reporting of percent and mmol/mol will continue. We believe that these issues should be resolved in the future and that it would avoid confusion if mmol/mol unit for HbA_1c were to gain worldwide acceptance.

A history of HbA1c through Clinical Chemistry and Laboratory Medicine

HbA(1c) was discovered in the late 1960s and its use as marker of glycemic control has gradually increased over the course of the last four decades. Recognized as the gold standard of diabetic survey, this parameter was successfully implemented in clinical practice in the 1970s and 1980s and internationally standardized in the 1990s and 2000s. The use of standardized and well-controlled methods, with well-defined performance criteria, has recently opened new directions for HbA(1c) use in patient care, e.g., for diabetes diagnosis. Many reports devoted to HbA1c have been published in Clinical Chemistry and Laboratory Medicine (CCLM) journal. This review reminds the major steps of HbA(1c) history, with a special emphasis on the contribution of CCLM in this field.

The general use of glycated haemoglobin for the diagnosis of diabetes and other categories of glucose intolerance: still a long way to go

Glycated haemoglobin (HbA(1c)) is considered the 'gold standard' for monitoring metabolic control in diabetes. An International Expert Committee recently recommended HbA(1c) as a better method than measurement of glucose to use in the diagnosis of diabetes, based on its strong association with microvascular complications, a lower day-to-day variability and ease of use, not necessarily in the fasting state. These recommendations have been embraced by the American Diabetes Association (ADA), which stated in its Standards of Medical Care in Diabetes 2010 that "A(1c), fasting plasma glucose or the 2 h 75 g oral glucose tolerance test (OGTT) are appropriate for testing diabetes and assessing the risk of future diabetes," and that "a confirmed A(1c) ≥ 6.5% is diagnostic for diabetes." Measuring HbA(1c) has several advantages over glucose measurements, but its exclusive use should only be considered if the test is conducted under standardised conditions and its limitations are taken into due account. The impact of its use on the epidemiology of diabetes and other categories of glucose intolerance, as seen from recent reports, is also discussed.

Glycated hemoglobin (HbA1c): old dogmas, a new perspective?

The hemoglobin A1c (HbA1c) assay provides a reliable measure of chronic glycemia and correlates well with the risk of long-term diabetes complications, so that it is currently considered the test of choice for monitoring and chronic management of diabetes. Recently, HbA1c testing has been included within the diagnostic criteria recommended for diagnosis of diabetes in nonpregnant individuals by the American Diabetes Association (ADA). The emerging concept that HbA1c can be used rather than blood glucose in the diagnosis of diabetes is highly appealing for a variety of reasons, including less sensitivity to preanalytical variables, lower within subject biological variability, little to null interference from diurnal variations, acute stress and common drugs which are known to influence glucose metabolism, as well as the fact that one single measurement might provide information for both diagnosing diabetes and tracking glycemic control. On the other hand, the use of HbA1c for screening and diagnosing diabetes also carries some limitations, including the worse diagnostic performance in different populations (i.e., pregnancy, elderly and non-Hispanic blacks), the risk of overdiagnosis in subjects with iron deficiency anemia, in subjects genetically predisposed to hyperglycation, and in those with increased red blood cell turnover. There is also a higher risk of misdiagnosis in patients with end-stage renal disease and heavy alcohol consumption. Finally, HbA1c testing might be biased due to the interference from several hemoglobin variants, is characterized by a higher imprecision than blood glucose measurement, and is more expensive. This paper will critically summarize the potential advantages and limitations of HbA1c as a recommended test for diagnosing diabetes.