Islet cell antibodies and glutamic acid decarboxylase antibodies, but not the clinical phenotype, help to identify type 1(1/2) diabetes in patients presenting with type 2 diabetes

This study was undertaken to determine which type 1 diabetes-associated aut oantibodies and what clinical characteristics are most useful to identify p atients with type 1 1/2 diabetes. We studied 125 patients, recently diagnos ed clinically with type 2 diabetes for the presence of islet cell antibodie s (ICA), insulin autoantibodies (IAA), antibodies to glutamic acid decarbox ylase(GADAb), and IA-2a (IA-2Ab). Patients with a diagnosis of type 2 diabe tes who met all of the following criteria at diagnosis were studied: age gr eater than or equal to 30 years, no history of ketonuria or ketoacidosis, a nd not requiring insulin treatment. Thirty-six patients (29%) were positive for at least 1 antibody. Thirty-two (26%) were ICA positive and 20 (16%) G ADAb positive. Insulin autoantibodies and IA-2Ab occurred less frequently i n 2 (1.6%) and 8 (6.4%) patients, respectively. There was no significant di fference in the ages at diagnosis between the Ab(+) and Ab(-) patients, age in years (range) 47.2 (32 to 64) versus 51.2 (31 to 77), respectively, P = .06. Body mass index (BMI) was different in the 2 groups, with Ab(+) patie nts being less obese, BMI (range) 28.3 kg/m(2) (17.6 to 54.9) versus 32.0 k g/m(2) (19.2 to 68.8), respectively, P = .01. Clinical presentation of diab etes was more commonly symptomatic with polyuria and polydipsia in Ab(+) pa tients, while in Ab(-) patients, diagnosis was more often incidental, P = . 002. However, more than 95% of patients overlapped in both age and BMI irre spective of antibody status. Similarly, 42% of Ab(+) patients had their dia betes diagnosed incidentally, while 29% of Ab(-) patients presented with po lyuria and polydipsia. We therefore conclude that screening with antibodies , mainly ICA and GAD, but not age, BMI, or clinical presentation should be used to identify type 1 1/2 diabetes. Copyright (C) 2001 by W.B. Saunders C ompany.