Heterozygous hemoglobin Hamadan affects HbA1c assay

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.

Glycemic monitoring in diabetics with sickle cell plus beta-thalassemia hemoglobinopathy

OBJECTIVE

To report a case of diabetes management in a patient with a hemoglobinopathy that caused her clinician to seek a different measure of glycemic control, fructosamine, rather than glycosylated hemoglobin (HbA1c).

CASE SUMMARY

A 53-year-old African American woman presented with a past medical history of type 2 diabetes, hypertension, seizure disorder, rheumatoid arthritis, and sickle cell disease plus beta-thalassemia. She reported fasting blood glucose values ranging broadly from 50 to 320 mg/dL, yet her HbA1c result remained steady in a low range of <6%. A measure of fructosamine returned elevated at 340 micromol/L (reference range 200-300).

DISCUSSION

We believe that this patient's hemoglobinopathy resulted in falsely low levels of HbA1c, and we substantiate this interpretation with the patient's self-monitored blood glucose values from home that appeared higher and inconsistent with the HbA1c results. Although few reports on using the measure of fructosamine appear in the literature, this patient's high fructosamine result supports fructosamine as the more appropriate measure of glycemic control.

CONCLUSIONS

Serum fructosamine levels may be considered as an appropriate laboratory measurement when monitoring long-term glycemic control in patients with type 2 diabetes mellitus and sickle cell disease.

Hemoglobin variants and determination of glycated hemoglobin (HbA1c)

Measurement of glycated hemoglobin in diabetic patients is an established procedure for evaluating long-term control of diabetes. The Diabetes Control and Complications Trial (DCCT), as well as the United Kingdom Prospective Diabetes Study (UKPDS), confirmed the direct relationship between the degree of glycemic control as estimated by glycohemoglobin (GHb) determinations and the development and progression of long-term complications in diabetic patients. Samples with known interferences of HbA(1c) determination as hemoglobinopathies are specifically excluded from certification testing and there are no guidelines or requirements for comparability of samples containing hemoglobin (Hb) variants. This paper reviews the interference of Hb variants on determination methods of glycated hemoglobin as they result in false HbA(1c) results.

Effects of Hemoglobin Variants and Chemically Modified Derivatives on Assays for Glycohemoglobin

Background: Glycohemoglobin (gHb), measured as hemoglobin (Hb) A1c or as total gHb, provides a common means for assessing long-term glycemic control in individuals with diabetes mellitus. Genetic variants and chemically modified derivatives of Hb can profoundly affect the accuracy of these measurements, although effects vary considerably among commercially available methods. The prevalence of genetic variants such as HbS, HbC, and HbE, and chemically modified derivatives such as carbamyl-Hb among patient populations undergoing testing is not insignificant. Clinical laboratories and sites responsible for point-of-care testing of gHb need to be aware of the interferences produced in assays by these Hbs.

Approach: We conducted a review of the literature describing the effects of variant Hbs on gHb assay methods commonly used in clinical laboratories.

Content: This review summarizes the documented effects of both common and uncommon Hb variants and derivatives on the measurement of gHb. Where known, we discuss mechanisms of interference on specific assays and methodologies. We specifically address effects of commonly encountered Hbs, such as carbamyl-Hb, HbS, HbC, HbE, and HbF, on assays that use cation-exchange chromatography, immunoassays, or boronate affinity methods for measuring gHb.

Summary: A variety of patient- and laboratory-related factors can adversely affect the measurement of gHb in patients harboring Hb variants or derivatives. Identification of the variant or derivative Hb before or during testing may allow accurate measurement of gHb by the selection of a method unaffected by the given variant or derivative. However, laboratories should make available alternative, non-Hb-based methods for assessing long-term glycemic control in individuals with HbCC, HbSS, or HbSC disease, or with other underlying disorders where the concentration of gHb does not accurately reflect long-term glycemic control.