Deceptive HbA1c in a patient with pure red cell aplasia

In September, 2008, a 59-year-old Japanese woman with pure red cell aplasia was diagnosed with diabetes mellitus by a haematologist, on the basis of a high concentration of HbA1c (8·2%). At the time of diagnosis, her fasting plasma glucose was 5·8 mmol/L. She immediately began taking acarbose, 300 mg daily. About 3 years later, she began sitagliptin, a dipeptidyl peptidase-4 inhibitor, at a daily dose of 50 mg. Her blood haemoglobin concentration remained low (50–70 g/L). Despite additional treatment with long-term blood transfusions (but not recombinant human erythropoietin), her HbA1c remained high (8·0%).