Testing for Autoimmunity and β -Cell Function in a Young Patient with Diabetes Mellitus

This is a case report of a 22-year-old Filipino male, morbidly obese, not known to have diabetes mellitus (DM) who presented with diabetic ketoacidosis on initial diagnosis. He had a phenotype of type 2 DM (T2D) but an initial presentation consistent with type 1 DM (T1D). Insulin therapy was eventually discontinued but he maintained good glycemic control with diet alone. C-peptide showed adequate increase after a mixed-meal diet and GAD65Ab was negative, thus he was diagnosed with ketosis-prone DM (KPDM). The increasing prevalence of obesity challenges the classic phenotype of patients with DM, with many patients presenting as an obese type T1D, and being diagnosed with T2D at a younger age. This complicates how to classify the patient’s diabetes, and the clinical profile is sometimes insufficient to make the proper diagnosis. In these cases, immunologic markers and assessment of β-cell function are important tools to differentiate between T1D and T2D, to direct management plans and to anticipate complications.