HbA1c and biomarkers of diabetes mellitus in Clinical Chemistry and Laboratory Medicine: ten years after

Since its discovery in the late 1960s, HbA_1c has proven to be a major biomarker of diabetes mellitus survey and diagnosis. Other biomarkers have also been described using classical laboratory methods or more innovative, non-invasive ones. All biomarkers of diabetes, including the historical glucose assay, have well-controlled strengths and limitations, determining their indications in clinical use. They all request high quality preanalytical and analytical methodologies, necessitating a strict evaluation of their performances by external quality control assessment trials. Specific requirements are needed for point-of-care testing technologies. This general overview, which describes how old and new tools of diabetes mellitus biological survey have evolved over the last decade, has been built through the prism of papers published in Clinical Chemistry and Laboratory Medicine during this period.

Comparison of glycation degrees of HbG-Coushatta and HbG-Taipei with HbA using liquid chromatography with tandem mass spectrometry

BACKGROUND

Hemoglobin A_1c(HbA_1c) is widely used to measure glycemic status and control in diabetes testing and treatment and is an important risk factor forcomplications of diabetes. Hemoglobin variants can interfere with the HbA_1c testing method by reducing the life span of erythrocytes or due to differences in glycation degrees. In this study, glycation levels of the HbA, HbG-Coushatta, and HbG-Taipei β-chains (βA, βG-Coushatta, and βG-Taipei, respectively) were examined.

METHODS

Blood samples from heterozygotic patients (HbG-Coushatta/HbA, HbG-Taipei/HbA) were analyzed. Glycation rateswere determined using high-performance liquid chromatography with tandem mass spectrometry. Ratios of glycated βG-Coushatta to glycated βA and glycated βG-Taipei to glycated βA were calculated by comparingareas under the curves from extracted ion chromatograms.

RESULTS

βG-Coushatta and βG-Taipei were 6.08 ± 1.38% and 5.95 ± 0.93% glycated (respectively), which were significantly higher than βA chains(4.55 ± 1.30% and 4.51 ± 0.91%, respectively; p = 0.000). The total glycation degree (α + β) in HbG-Coushatta and HbG-Taipei heterozygotes were estimated to be 9% and 8% higher than those of HbA homozygotes (P＜0.001), respectively.

CONCLUSION

βG-Coushatta and βG-Taipei glycation degrees were significantly higher than βA, while the differences in total hemoglobin (α + β) were small and unlikely to impact the clinical interpretation of HbA_1c results.

Association of hemoglobin H (HbH) disease with hemoglobin A1c and glycated albumin in diabetic and non-diabetic patients

OBJECTIVES

Hemoglobin A_1c (HbA_1c) and glycated albumin (GA) are glycemic control status indicators in patients with diabetes mellitus. Hemoglobin H (HbH) disease is a moderately severe form of α-thalassemia. Here we examine the usefulness of HbA_1c and GA in monitoring glycemic control in patients with HbH disease.

METHODS

HbA_1c, GA, and an oral glucose tolerance test were performed in 85 patients with HbH disease and 130 healthy adults. HbA_1c was measured using five methods, including two systems based on cation-exchange high-performance liquid chromatography (Variant II Turbo 2.0 and Bio-Rad D100), a capillary zone electrophoresis method (Capillarys 3 TERA), a boronate affinity HPLC method (Premier Hb9210), and an immunoassay (Cobas c501).

RESULTS

Significant lower levels of HbA_1c were observed in patients with HbH disease than in healthy adults. In contrast, GA showed no statistically significant differences between participants with and without HbH disease. A considerable number of diabetic patients with HbH disease would be missed if using HbA_1c as a diagnostic criterion for diabetes mellitus.

CONCLUSIONS

GA but not HbA_1c is suitable for monitoring glycemic control in patients with HbH disease that can modify the discriminative ability of HbA_1c for diagnosing diabetes.

Potential of MALDI-TOF mass spectrometry to overcome the interference of hemoglobin variants on HbA1c measurement

Objectives

Hemoglobin (Hb) variants remain an important cause of erroneous HbA1c results. We present an approach to overcome the interference of Hb variants on HbA1c measurements using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS).

Methods

Samples containing or not containing Hb variants were analyzed for HbA1c using an MALDI-TOF MS system (QuanTOF) and a boronate affinity comparative method (Ultra2). For QuanTOF, two sets of HbA1c values were obtained through α- and β-chain glycation.

Results

A robust correlation between the glycation degrees of the α- and β-chains was found, and HbA1c values derived from α- and β-chain glycation correlated well with the Ultra2 results. Statistically significant differences (p<0.01) were found for all the Hb variants tested. When using the conventional β-chain glycation to determine HbA1c, clinically significant differences were only found among samples containing β-chain variants detected by QuanTOF (i.e., Hb J-Bangkok, Hb G-Coushatta, and Hb G-Taipei). In contrast, based on α-chain glycation, no clinically significant differences were found for these three variants.

Conclusions

In addition to conventional β-chain glycation, α-chain glycation can be used to calculate HbA1c values. The interference of Hb variants on HbA1c quantification can be overcome by employing the glycation of the globin chain without a genetic variant to estimate HbA1c values.

Recognition of rare hemoglobin variants by hemoglobin A1c measurement procedures

BACKGROUND

Unrecognized hemoglobinopathies can lead to measured hemoglobin A_1c (Hb A_1c) concentrations that are erroneous or misleading. We determined the effects of rare hemoglobin variants on capillary electrophoresis (CE) and HPLC methods for measurement of Hb A_1c.

METHODS

We prospectively investigated samples in which Hb A_1c was measured by CE during a 14-month period. For samples in which the electropherograms suggested the presence of rare hemoglobinopathies, hemoglobin variants were identified by molecular analysis or by comparison with electropherograms of known variants. When sample volume permitted, Hb A_1c was measured by 2 HPLC measurement procedures and by boronate affinity HPLC.

RESULTS

Hb A_1c was measured by CE in 33,859 samples from 26,850 patients. 15 patients (0.06%) were identified as having rare hemoglobinopathies: Hbs A2 prime, Agenogi, Fannin-Lubbock I, G Philadelphia, G San Jose, J Baltimore, La Desirade, N Baltimore, Nouakchott, and Roanne. Among 6 of these samples tested by 2 ion-exchange HPLC methods, the rare Hb was detected by both HPLC methods in only one sample, and none were detected by boronate affinity HPLC. The mean of the Hb A_1c results of 2 HPLC methods differed from the result of the CE method by 0.7-2.2% Hb A_1c in samples with variant hemoglobins versus <0.2% Hb A1c in samples without variants.

CONCLUSION

Measurement procedures differ in the ability to detect the presence of rare Hb variants and to quantify Hb A_1c in patients who harbor such variants.

Effects of α-Thalassemia on HbA1c Measurement

BACKGROUND

α-Thalassemia is a benign condition that is often present in patients with diabetes mellitus. Here, we evaluated the effects of different genotypes α-thalassemia on HbA_1c measurement.

METHODS

A total of 189 samples from nondiabetic patients were analyzed. HbA_1c analysis was performed by ion-exchange high-performance liquid chromatography, boronate affinity HPLC, immunoassay, and capillary electrophoresis. Fasting glucose, fructosamin, and HbA₂ were also performed. All samples were confirmed by genotyping for thalassemia.

RESULTS

In patients with two or three functional α-genes, HbA_1c values were not significantly different from those of controls (P > 0.05); however, in individuals with α-thalassemia with one functional α-gene (i.e., HbH disease), HbA_1c levels were significantly different from those of controls (P < 0.01). HbA_1c values were significantly lower in individuals with HbH disease than in control individuals and patients in the other two α-thalassemia groups. For patients with HbH disease, there were no significant differences in the four HbA_1c measurement systems (P > 0.05).

CONCLUSIONS

In this study, HbA_1c values in samples from individuals with two or three functional α-genes basically reflected the normal mean blood glucose level, while those in samples from individuals with one functional α-gene did not.