Elevated haemoglobin A1c confounds thalassaemia diagnosis by lowering HbA2 levels

<b>Background:</b> Thalassemias are inherited disorders caused by reduced production of structurally normal haemoglobin chains. Haemoglobin A2 (HbA2) constitutes an important parameter in the diagnostic evaluation of thalassaemias. Insight into the factors that modulate HbA2 levels is critical for correct interpretation of laboratory results in cases where thalassaemia is suspected. <b>Methods:</b> A retrospective study was conducted on patients who underwent haemoglobin analysis by high-performance liquid chromatography (HPLC) at Amsterdam UMC. Patients with elevated haemoglobin A1c (HbA1c) levels due to chronic hyperglycaemia were compared with controls, an iron deficiency cohort, and α-thalassemia cohorts. <b>Results:</b> Patients with strongly elevated HbA1c levels (110-180 mmol/mol) showed significantly reduced HbA2 levels compared with controls (2.0% vs. 2.4%, <i>P</i><0.0001). This reduction in HbA2 fraction was not observed when HbA2 was expressed relative to non-glycated HbA instead of all haemoglobin fractions. Red cell indices (MCH, MCV) and haemoglobin concentrations remained unaffected. The degree of HbA2 reduction in patients with high HbA1c was comparable to that observed in iron deficiency and α-thalassemia. <b>Conclusions:</b> Elevated HbA1c levels due to chronic hyperglycaemia lower measured HbA2 fractions, confounding the diagnostic evaluation of thalassaemias. Laboratories should consider HbA1c status when interpreting HbA2 results in patients with poorly controlled diabetes. Expressing HbA2 relative to non-glycated HbA may improve diagnostic accuracy in such cases.