Adult-onset autoimmune diabetes identified by glutamic acid decarboxylase autoantibodies: a retrospective cohort study

Patients with GAD antibodies (GADAb) showing clinical features of type 2 diabetes typically exhibit progression to an insulin-dependent state in several months or years. This condition is diagnosed as slowly progressive insulin-dependent (type 1) diabetes mellitus (SPIDDM) or latent autoimmune diabetes in adults, a subtype of adult-onset autoimmune diabetes. However, some patients diagnosed with adult-onset autoimmune diabetes do not progress to an insulin-dependent state. We conducted a retrospective cohort study to identify patients with non-insulin-dependent diabetes among those diagnosed with adult-onset autoimmune diabetes using measurable indicators in routine clinical practice. We surveyed data from the electronic medical records of all patients with GADAb from eight medical centres in Japan for selecting and analysing patients who matched the diagnostic criteria of SPIDDM. Overall, 345 patients were analysed; of these, 162 initiated insulin therapy (insulin therapy group), whereas 183 did not (non-insulin therapy group) during the follow-up period (median 3.0 years). Patients in the non-insulin therapy group were more likely to be male and presented a later diabetes onset, shorter duration of diabetes, higher BMI, higher blood pressure levels, lower HbA1c levels, lower GADAb levels and lesser antidiabetic agent use than those in the insulin therapy group when GADAb was first identified as positive. A Cox proportional hazards model showed that BMI, HbA1c levels and GADAb levels were independent factors for progression to insulin therapy. Kaplan–Meier analyses revealed that 86.0% of the patients with diabetes having GADAb who presented all three factors (BMI ≥ 22 kg/m2, HbA1c