High-titer autoantibodies against glutamic acid decarboxylase plus autoantibodies against insulin and IA-2 predicts insulin requirement in adult diabetic patients.

Antibodies against glutamic acid decarboxylase (GADA) is known to be a good predictive marker for insulin-dependency among adult diabetic patients. However, since not all of the GADA-positive patients will develop insulin requirement, we investigated whether other markers, that is, antibodies against IA-2 (IA-2A), insulin autoantibodies (IAA) and HLA class II type, would affect its predictive value for insulin requirement. Adult diabetic patients in the non-insulin-requiring stage were screened for GADA and registered in the study if positive. At the end of the follow-up period, 15 of the 43 GADA-positive patients required insulin. Among GADA-positive patients, the GADA titers of the insulin-requiring patients were significantly higher (199 U vs. 5.8 U, P<0.001) and high-titer GADA was more frequently detected among insulin-requiring patients (80%vs. 11%, P<0.0001). IAA was more frequently detected in insulin-requiring patients (40%vs. 0%, P<0.001), and IA-2A was detected only among insulin-requiring patients. Combinations of these three antibodies (GADA with either IAA or IA-2A) had 100% positive predictive value. In conclusion, the GADA test is a good screening test for predicting insulin requirement in adult diabetic patients and both the IAA and IA-2A tests are useful second line tests.