Unexpected HbA1c results in the presence of three rare hemoglobin variants

Interference of hemoglobin variants with HbA1c measurements: comparison of 6 commonly used HbA1c methods with the IFCC reference method

BACKGROUND

Glycated hemoglobin, or hemoglobin A1c (HbA1c), serves as a crucial marker for diagnosing diabetes and monitoring its progression. We aimed to assess the interference posed by common Hb variants on popular HbA1c measurement systems.

METHODS

A total of 63 variant and nonvariant samples with target values assigned by the International Federation of Clinical Chemistry and Laboratory Medicine (IFCC) reference method were included. We assessed 6 methods for measuring HbA1c in the presence of HbS, HbC, HbD, HbE, and fetal hemoglobin (HbF): 2 cation-exchange high-performance liquid chromatography (HPLC) methods (Bio-Rad D-100 and HLC-723 G8), a capillary electrophoresis (CE) method (Sebia Capillarys 3 TERA), an immunoassay (Roche c501), an enzyme assay system (Mindray BS-600M), and a boronate affinity method (Primus Premier Hb9210).

RESULTS

The HbA1c results for nonvariant samples from the 6 methods were in good agreement with the IFCC reference method results. The Bio-Rad D-100, Capillarys 3, Mindray BS-600M, Premier Hb9210, and Roche c501 showed no interference from HbS, HbC, HbD, and HbE. Clinically significant interference was observed for the HLC-723 G8 standard mode. Elevated HbF levels caused significant negative biases for all 6 methods, which increased with increasing HbF concentration.

CONCLUSION

Elevated levels of HbF can severely affect HbA1c measurements by borate affinity, immunoassays, and enzyme assays.

Hb Hebei [α20 (B1) His→Leu; HBA2:C.62A > T]: A Novel Hemoglobin Variant Found during Measurement of Glycated Hemoglobin

We report a novel hemoglobin (Hb) variant found in a 34-year-old Chinese male during a routine measurement of glycated hemoglobin. The variant resulted in a P3 peak of 27.5% of the total Hb on high performance liquid chromatography (HPLC) with a glycated hemoglobin mode. However, no abnormal Hb peaks were observed in capillary electrophoresis (CE) with 3.1% Hb A2 and 96.9% Hb A. The amino acid substitution was determined by Sanger sequencing as α20 (B1) His→Leu; the corresponding DNA mutation was identified as CAC > CTC at the first position of codon 20 of the α-chain. This is the first description of the mutation, and we have named it Hb Hebei for the region of origin of the proband.

Interference of hemoglobin variants in HbA1c quantification

Fasting blood glucose and glycated hemoglobin (HbA_1c) are routine biomarkers to screen and monitor diabetes mellitus. HbA_1c results from glycation at the N-terminus of the β globin chain of tetrameric human hemoglobin. Fasting blood glucose level varies with the nature and amount of food intake, physical exercise, etc., and, accordingly, is a short-term measure of glucose control. In contrast, HbA_1c provides an average measure of glucose control for the long-term (8-12 weeks). Unfortunately, genetic variants of hemoglobin may interfere with HbA_1c quantification using ion exchange chromatography, capillary electrophoresis, immunoassay and boronate affinity chromatography. Mass spectrometry, however, measures total glycation of hemoglobin across both α and β globin chains and correlates well with the ion exchange based method. Additionally, mass spectrometry based quantification is not impacted by the presence of genetic variants of hemoglobin and thus might be a better analytical choice for diabetes mellitus.

False hemoglobin A1c value as a result of compound heterozygotes of hemoglobin E and hemoglobin New York

The presence of hemoglobin (Hb) variants might interfere with some glycated hemoglobin (HbA_1c ) measurements. There have been a few reports of compound Hb variants affecting HbA_1c testing. Here, we report a case of the coinheritance of two Hb variants in the β-globin gene. High-performance liquid chromatography with the Hb program showed a high HbA₂ level. Similarly, an E-window peak was separated on the high-performance liquid chromatography with a glycated Hb program. However, capillary electrophoresis showed two abnormal peaks and no HbA peak. Sanger sequencing confirmed the presence of Hb New York and HbE. This is the first report of a compound heterozygote for HbE and Hb New York. The double heterozygote caused erroneous results for HbA_1c on high-performance liquid chromatography and enzyme assay.

Hemoglobin J in a patient with severe anemia, a case report from Nepal

Introduction

Hemoglobin J is defined by a faster movement towards anode when compared with the normal hemoglobin A. Though a pathologically distinct entity from the normal HbA, it remains clinically silent due to little physiological difference as exemplified by a similar oxygen binding capacity between the two. Though cases of symptomatic HbJ have been reported, it is uncommon. Hence, further explanations should be sought in such cases.

Case presentation

Our case report exemplifies the presence of an alpha thalassemia trait along with HbJ in a symptomatic case of anemia from rural Nepal.

Discussion

CE-HPLC complemented by electrophoresis, is the method of choice for characterizing various hemoglobin variants including Hb J. Hb J presents as elevated P3 peak on HPLC while thalassemia is detected by the presence of eluted proteins at the retention time between 0 and 1 minutes. P3 peak up to 6% is considered normal, values 6%–12% indicates suboptimal specimen and values greater than 15% indicates Hb J.

Conclusion

Variants of hemoglobin including HbJ variant is detected using HPLC technique. Mostly clinically silent, if HbJ is associated with anemia, search for a concomitant cause should be sought one of them being alpha thalassemia when iron deficiency has been ruled out by a serum iron profile.

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HbJ is rare variant of hemoglobin with 71 nrw variants till date.

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CE-HPLC stands as a standard for these hemoglobin variants differentiation where Hb J presents as a P3 peak.

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Anemia when associated with HbJ should be searched for concomitant hemoglobinopathy