[Effects of hemoglobin J-Bangkok traits on measurements of glycated hemoglobin by five methods]

[Effects of Hemoglobin Variants on Glycosylated Hemoglobin Testing]

Objective

To examine the common types of hemoglobin variants and to evaluate the influence of common variants on the results of two kinds of glycosylated hemoglobin (HbA1c) tests.

Methods

We conducted a retrospective study, analyzing the data of a patient population undergoing two HbA1c tests, high performance liquid chromatography (HPLC) and capillary electrophoresis (CE), at West China Hospital, Sichuan University between March 2021 and February 2022. By screening the chromatograms, the hemoglobin variants were identified and their migration positions in the CE method were recorded. The effects of the variants with different migration positions on the findings of the two methods were compared. Variant samples with different migration positions were selected and Sanger sequencing was performed to determine mutations in HBA1, HBA2, and HBB genes in the variant samples.

Results

We examined the HbA1c of 207 786 patient samples, identifying variant peaks in the chromatograms of 372 patients. The detection rate of variants was 0.18%, with the variant identification rate of HPLC being 43.3% and that of CE, 100%. Through sequencing, 20 variants were detected. A total of 261 patient samples were tested for HbA1c with both HPLC and CE. HPLC reported all HbA1c results, while CE did not report HbA1c results for 28 samples, among which, 26 showed abnormal peaks that overlapped with HbA1c peaks, and 2 showed abnormal peaks that overlapped with HbA0 peaks. The commonly observed variant migration positions, as revealed by CE, were at the horizontal coordinates of 225±1, 200±3, 100±2, 124±1, 70±2, and 182±1. There was significant difference between HPLC method and CE method in the determination of HbA1c ( P<0.0083), and the difference between the two methods was the largest when there were variants in the 200±3 region. Linear regression showed that the correlation of HbA1c results between the two methods was different when different regional variants were present, and that the correlation between the two methods was strongest when 124±1 region was present ( r=0.998).

Conclusion

There are diverse types of hemoglobin variants and most of them can affect the HbA1c findings of HPLC. Analyzing the chromatogram facilitates the identification of the variants.

False measurement of glycated hemoglobin in patients without hemoglobin A

Background: Hemoglobin (Hb) A_1c, a biochemical marker widely used in monitoring diabetes mellitus, can be quantitatively measured by various examining systems. However, significant errors still exist. In the present study, we evaluated the HbA_1c level in five patients with compound heterozygotes by five different examining systems and our goal is to identify the existence of erroneous HbA_1c measurement.Methods: Blood samples collected from normal (no hemoglobin variants) and abnormal (compound heterozygotes) patients were analyzed by capillary electrophoresis technique and sequence analysis. The samples without HbA expression via above methods were further analyzed for HbA_1c by ion exchange HPLC Variant II/ Variant II Turbo 2.0 (VII and VII-T 2.0), boronate affinity HPLC, capillary electrophoresis, and Tinaquant immunoassay.Results: HbA_1c expression were unexpectedly detected in the compound heterozygous samples by using additional examining systems: The HPLC VII and VII-T 2.0 detected HbA_1c expression in two of five samples and failed to detect the abnormal HbA₂ expression; the CE system detected HbA_1c expression in one of five samples with abnormal HbA₂ expression; the Ultra2 and PPI system detected the HbA_1c expression of all samples without abnormal HbA₂ Conclusions: Five human samples without HbA expression were additionally detected with HbA_1c expression with or without abnormal HbA₂ expression by five analysis systems and the different examining assay potentially affected the test results. These results demonstrated that the limitations of current examining systems for monitoring patients with hemoglobin disorders highlighting the further improvement in the method of clinical HbA examination.