Background: LADA is a subgroup of type 1 diabetes mellitus characterized by its age at diagnosis being more than 30 years, presence of Glutamic Acid Decarboxylase₆₅ (GAD₆₅) autoantibody, and insulin independency in the first 6 months of diagnosis. Our aim was to determine the prevalence and predictors of LADA in a large population-based drug naïve newly diagnosed adult diabetics of Tehran urban population.

Methods: In this cross-sectional study, all newly diagnosed diabetics of Tehran Lipid and Glucose Study aged more than 30 years who were not initialy treated with insulin were tested for GAD antibody titer. Thirty two GAD antibody positive (LADA) and 556 GAD antidody negative patients (type 2 diabetics) were found and compared for anthropometric, clinical and laboratory features.

Results: Mean age of all 588 cases was 54.2±11.6. The prevalence of LADA was %5.44 (CI %95: %3.6-%7.3). Age, sex, BMI, family history of diabetes, diastolic blood pressure, glucose and lipid profile and the prevalence of metabolic syndrome were similar between LADA and type 2 diabetics. Systolic blood pressure were greater in type 2 diabetics than in LADA group. No model could predict the result of GAD antibody measurement.

Conclusion: autoimmune process is present in early stages of diabetes in %5.4 of newly diagnosed adult diabetics assumed to suffer type 2 diabetes mellitus. Using clinical and laboratory features, no model could reliably screen these cases. It seems reasonable to test GAD antibody in all such cases to early find persons more probable to have a more rapid process toward pancreas insufficiency.