Seroconversion of Glutamic Acid Decarboxylase Antibodies in a Patient Initially Diagnosed as Having Type 2 Diabetes Mellitus

A 61-year-old man admitted in July 1998 had suffered from thirst, polydipsia and polyuria for three years. Diet and transient insulin therapy had induced good blood glucose control which was maintained by metformin hydrochloride for a year. Although it worsened, conventional insulin treatment re-implemented good blood glucose control. Glutamic acid decarboxylase antibodies (GAD-Ab) had been negative up to this point. After 8 months, blood glucose levels became elevated. To date, the GAD-Ab has been positive (112-120 U/ml), and the serum and urine C-peptide levels are decreased. Seroconversion of GAD-Ab should be noted in patients initially diagnosed as having GAD-Ab negative type 2 diabetes mellitus.