Glycosylated haemoglobin: a false sense of security.

We report the unusual case of a patient found to have a low glycosylated haemoglobin (HbA1c) despite having recently been diagnosed with diabetes mellitus type 2. The patient, who was not anaemic, with no symptoms or family history of haematological conditions, was subsequently found to have an elevated reticulocyte count, inferring increased red cell turnover as the culprit for the discordant HbA1c result. A diagnosis of hereditary spherocytosis was made based on characteristic peripheral blood film appearances and confirmed by eosin-5-maleimide binding test. Exposure of an undiagnosed haemolytic anaemia by virtue of a low HbA1c is uncommon. However, conditions that distort HbA1c measurements are not infrequent. This case should serve to remind clinicians of the limitations of HbA1c in specified situations, and to remain vigilant when interpreting results.