Interference of dapsone in HbA1c monitoring of a diabetic patient with polychondritis.

A 80-year-old man was regularly surveyed in our service since 1987 for a relapsing polychondritis and treated with Dapsone, 100 mg per day, with a good outcome on chondritis. During the follow-up, a prostate carcinoma was diagnosed in 1990 and treated with surgery and brachytherapy. An in situ bladder carcinoma was treated in 1997 with BCG therapy. Both carcinomas were regularly surveyed and remained controlled: PSA was < 0.5 ng/mL (N < 4), periodic bladder cytologies showed no malignant cells. Biological survey showed a normal red blood cell count with a mild hemolysis [bilirubin = 35 mMol/L (0 < N < 17), LDH = 350 UI/L (150 < N < 320) and reticulocytosis 155 × 10/L] due to a chronic Dapsone-induced methemoglobinemia which was evaluated around 2%. In 1999, fasting glycemia was controlled several times around 1.3 g/L (7.4 mMol/L) checked on 100 UI/mL and 30UI/mL lithium heparinate test-tubes. Fasting insulinemia was normal at 6 mMol/L (4 < N < 6) and HbA1c was in the normal range: 4.2% (N < 6.5%). Proteinuria was about 0.23 g/24 h and albuminuria around 58 mg/24 h (microalbuminuria). Diet was proposed and compliance was good during two years. At the last visit in January 2002, he complained of polydypsia, polyuria and weight loss. Fasting glycemia was 1.7 g/L (9.5 mMol/L). Several fasting glycemia were controlled per 24 hours. At 7 AM fasting glycemia was 1.93 g/L (10.7 mMol/L). At 10 AM 2.07 g/L (11.5 mMol/L). At 15 PM fasting glycemia was 2.52 g/L (14 mMol/L). At18 PM fasting glycemia was 2.07 g/L (11.5 mMol/L). Glycated hemoglobin (HbA1c) was still normal: 4%. Insulinemia and plasma level of peptide C were also normal. Faced with such features, antidiabetic treatment with acarbose (Glucort) was begun with a good outcome on clinical symptoms and glycemia. Since then, evaluation of long-standing glycemic control was based on fructosamine concentration and remained correct.