Methods, units and quality requirements for the analysis of haemoglobin A_1cin diabetes mellitus

Abstract

The formation of glycohemoglobin, especially the hemoglobin A1c (HbA1c) 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 HbA1C because they have elevated blood glucose concentrations. Thus HbA1c has acquired a very important role in the treatment and diagnosis of diabetes mellitus. After the introduction of the first quantitative measurement OF HbA1C, 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 HbA1c 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 HbA1c 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 HBA1c measurement. When the reference procedures were established, in 2004 IFCC recommended that all manufacturers for equipment used in HbA1c 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 HbA1c assays, analytical problems, problems with the units in which HbA1c values are expressed, reference values, quality control aspects, target requirements for HbA1c, and the relationship of the plasma glucose values to HbA1c concentrations. We also note that the acceptance of the mmol/mol system for HbA1c 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 HbA1c 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 HbA1c were to gain worldwide acceptance.

Hemoglobin A(1c) Reporting Units and Diagnostic Cut-Offs in Relation to International Recommendations

“…Several questionnaires have been sent to societies of laboratory medicine starting from 2009. The replies after the data collection from 2009 to 2017 are presented in Table 2, indicating the use of HbA(1c) units [2]. The number of answers increased as of 2009 as compared to previous years (e.g.…”

“…The annual HbA(1c) rounds of Labquality Ltd. were performed four to six times per year using two native EDTA blood samples, one close to the level of HbA(1c) at the diagnostic level recommended by the ADA, namely 6.5% (48 mmol/mol), and the second typically at a moderately elevated HbA(1c) level [2,12,15]. Only the results from the native EDTA blood samples were used for this study as their variation is smaller than that of commercial liquid samples.…”

“…In addition, in 1994, 60% of the HbA1(1c) analyses were performed using liquid chromatography, but in 2017 this figure had decreased to 29% (Table 1). There was thus a continuous transition from chromatography to immunochemistry [2,15].…”

“…There are 5.5 million inhabitants in Finland, of which about half a million suffer from diabetes mellitus (DM), and the number is constantly rising [1]. DM mainly affects the nervous, muscle, kidney, and ocular tissues by changing glucose metabolism [1,2]. Previously DM was diagnosed by glucose concentration in the blood or urine.…”

“…Later in the 1960s, measurement of the hemoglobin A(1c) fraction by qualitative or quantitative assays began when Trivelli & al. published the first quantitative assay of HbA(1c) [3,4]. Numerous methods have then been developed for HbA(1c) measurements [2,[4][5][6][7]. Weykamp & al concluded that the high variation between the methods and the laboratories was substantially corrected by a new calculation of the primary results [5].…”