Variability in Autoantibody Ordering Patterns Suggests Potential for Diabetes Misclassification

OBJECTIVE Many adults with type 1 diabetes (T1D) are misclassified as having type 2 diabetes (T2D). Islet autoantibodies inform diabetes classification; however, discerning which adults should be tested is challenging due to the high prevalence of T2D. We aimed to evaluate and compare islet autoantibody testing in children and adults and characterize individuals who underwent diabetes reclassification following testing. RESEARCH DESIGN AND METHODS Using the electronic health record system of an academic medical center, we identified individuals who were evaluated for islet autoantibodies (GAD65, islet antigen 2, insulin autoantibody, and zinc transporter 8) between July 2024 and June 2025. We compared ordering patterns in children and adults, quantified islet autoantibody positivity, and characterized individuals whose diabetes was reclassified to T1D after islet autoantibody testing. RESULTS Among 1,077 individuals undergoing islet autoantibody testing for diabetes classification and screening, 976 had a diabetes diagnosis, 74% of whom had preexisting diabetes and 26% had new-onset diabetes. Altogether, 309 individuals had positive islet autoantibodies. While 51% of children were tested in endocrinology clinics and 65% had four islet autoantibodies drawn, 36% of adults were evaluated in endocrinology and only 6% had four islet autoantibodies tested. Following testing, 91 people (13%) were reclassified as having T1D, of whom 89% were >18 years old and of whom 51% went >5 years before receiving a T1D diagnosis. CONCLUSIONS This real-world data analysis demonstrates that islet autoantibody testing is more consistent in children than adults with diabetes, raising the risk of diabetes misclassification. Better tools are needed to support islet autoantibody ordering in adults.