Incidental findings of variant hemoglobin during hemoglobin A(1c) testing

Structural hemoglobinopathies: Analysis of 128 cases and their relevance in the diabetic control

BACKGROUND AND OBJECTIVES

Hemoglobinopathies are monogenic disorders with autosomal recessive inheritance. In Europe, with increased migration flows these conditions are appearing more frequently in non-endemic regions. HbA_1c testing is useful for evaluating long-term glycaemic status in diabetes mellitus patients. During HbA_1c evaluation, other hemoglobin fractions are detected, such as structural hemoglobinopathies. The principal objective of this work is to study the incidence of structural hemoglobinopathies in our area and their management.

MATERIAL AND METHODS

Total population of 65,000 patients for glycaemic monitoring was evaluated with HPLC equipment (HPLC-ARKRAY® ADAMS, Menarini Diagnostics, Italy). This equipment quantifies different hemoglobin fractions.

RESULTS

We identified a total of 128 variants, representing an incidence with respect to the study population of 0.19% (1.97‰). Most (69) were identified in the foreign population, and the most frequent variant identified was heterozygous S hemoglobinopathy. In six families, structural hemoglobinopathy was identified. Three patients with HbS/HbS were detected. Primary Health Centers were the origin of an important part of these variants (82).

CONCLUSIONS

Our study describes a low incidence for structural variants compared with the estimated incidence in Spain. These variants can interfere with HbA_1c testing. In these cases, glycated protein study is an appropriate alternative to monitor diabetic therapy.

Hemoglobin S monitoring on TOSOH G8 in hemoglobin A1c mode in case of urgent red blood cell exchange

BACKGROUND

Pre- and post-transfusion hemoglobin S (HbS) levels are used to document the efficacy of red blood cell exchange (RCE) in patients with sickle cell disease (SCD). In case of urgent RCE a 24/7 short turn-around time (STAT) analysis, with the ability to identify and quantify HbS, is warranted. The use of TOSOH G8 (Tosoh Europe) is evaluated for this purpose, using the variant HbA1c mode.

METHODS

Analytical performance of the HbS analysis on TOSOH G8 in variant HbA1c mode was evaluated, including assessment of imprecision and linearity for HbS. In addition, a comparison study between TOSOH G8 and Minicap Flex Piercing (FP) system CZE (Sebia) using 32 HbS samples (HbS range: 9%-93%) was carried out to evaluate analytical and clinical concordance.

RESULTS

Total HbS imprecision was 1.77% and 0.31% for a sickle cell trait and a sickle cell anemia sample, respectively. An acceptable linearity (HbS range: 6%-88%) was observed (R²  > .99). Passing-Bablok regression analysis showed a significant proportional bias; however, a good analytical concordance (r > .95) was found. Our results suggested that TOSOH G8 underestimated HbS results compared with those of Minicap FP system (mean difference: -3.54%), especially in samples with a high HbS concentration.

CONCLUSION

Hemoglobin S results obtained with TOSOH G8 in variant HbA1c mode are clinically acceptable to monitor urgent RCE. The observed underestimation will not alter clinical decision-making.

Haemoglobin variants may cause significant differences in haemoglobin A1c as measured by high-performance liquid chromatography and enzymatic methods in diabetic patients: a cross-sectional study

Background We aimed to determine whether the discrepancy between haemoglobin A1c values determined by high-performance liquid chromatography and enzymatic haemoglobin A1c measurements in diabetic patients was clinically relevant. Methods We randomly recruited 1421 outpatients undergoing diabetic treatment and follow-up who underwent at least three haemoglobin A1c measurements between April 2014 and March 2015 at our clinic. In 6369 samples, haemoglobin A1c was simultaneously measured by HA-8160 and MetaboLead (enzymatic assay), and the values were compared. Results haemoglobin A1c measurements by high-performance liquid chromatography and enzymatic assay were strongly correlated (correlation coefficient: 0.9828, linear approximation curve y = 0.9986x - 0.2507). Mean haemoglobin A1c (6.8 ± 1.0%) measured by high-performance liquid chromatography was significantly higher than that measured by enzymatic assay (6.5 ± 1.0%, P < 0.0001). During the sample processing, four (0.3%) subjects presented consistently lower haemoglobin A1c values (<0.7%) by high-performance liquid chromatography than those from enzymatic assay. Of these, three had Hb Toranomon [β112 (G14) Cys→Trp]. The fourth had Hb Ube-2 [α68 (E17) Asn→Asp]. One other subject presented consistently higher haemoglobin A1c values (>1%) by high-performance liquid chromatography than those from enzymatic assay and was diagnosed with a -77 (T > C) mutation in the δ-globin gene. These unrelated asymptomatic subjects had normal erythrocyte profiles, without anaemia. Conclusions We showed that haemoglobin A1c values measured by high-performance liquid chromatography were significantly higher than those measured by enzymatic assay in diabetic subjects. However, when an oversized deviation (>0.7%) between glycaemic control status and haemoglobin A1c is apparent, clinicians should check the methods used to measure haemoglobin A1c and consider the possible presence of a haemoglobin variant.