Routine islet autoantibody testing in clinically diagnosed adult-onset type 1 diabetes can help identify misclassification and the possibility of successful insulin cessation.

Objective Recent joint American and European diabetes association guidelines recommend routine islet autoantibody testing in all adults newly diagnosed with type 1 diabetes. We aimed to assess the impact of routine islet autoantibody testing in this population. Research Design and Methods We prospectively assessed the characteristics and progression (annual change in Urine C-peptide Creatinine Ratio (UCPCR)) associated with islet autoantibody status (GAD, IA-2 and ZNT8) in 722 adults (≥ 18 years old at diagnosis) with clinically diagnosed type 1 diabetes and duration Results 24.8% (179/722) of participants diagnosed with type 1 diabetes were autoantibody negative. This group had genetic and C-peptide characteristics suggestive of a high prevalence of non-autoimmune diabetes: lower mean type 1 diabetes genetic risk score (islet autoantibody negative versus positive: 10.85 vs 13.09 (pp After median 24-months follow up, treatment change occurred in 36.6% (60/164) of autoantibody negative participants: 22.6% (37/164) discontinued insulin, with a HbA1c similar to those continuing insulin (57.5 vs 60.8mmol/mol [7.4 vs 7.7%], p=0.4) and 14.0% (23/164) added adjuvant agents to insulin. Conclusions In adult-onset clinically diagnosed type 1 diabetes, negative islet autoantibodies should prompt careful consideration of other diabetes subtypes. When routinely measured negative antibodies are associated with successful insulin cessation. These findings support recent recommendations for routine islet autoantibody assessment in adult-onset type 1 diabetes.