Type 1 Diabetes Is Not Just a Pediatric Problem

Many adults with diabetes are incorrectly diagnosed because of an assumption that type 1 diabetes is a pediatric condition. In fact, incidence and prevalence rates of adult-onset type 1 diabetes are higher than those of childhood-onset type 1 diabetes. Too often, when we diagnose diabetes in adults, we automatically assume that they have type 2 diabetes. Approximately 62% of new type 1 diabetes diagnoses made in 2021 occurred in people ≥20 years of age (1,2). Currently in the United States, 2 million people have type 1 diabetes, including about 304,000 children and adolescents (3).

The presentation of adult-onset type 1 diabetes is more heterogenous than its presentation in childhood, and adults with the disease may be asymptomatic. Exogenous insulin may not be required at diagnosis, although individuals may present with typical symptoms of insulin deficiency. The overlap of clinical and pathogenic features of type 1 and type 2 diabetes in people with adult-onset type 1 diabetes makes it difficult to distinguish between these conditions. Hence, misdiagnosis is common (4,5). A commentary published in this issue of Clinical Diabetes (p. 128) focuses on the related issue of “double diabetes” (6).

A significant differentiating factor is that multiple type 1 diabetes–associated islet autoantibodies typically develop. In fact, β-cell–specific autoimmunity with GAD65 autoantibodies is more frequently detected in adult-onset than in childhood-onset type 1 diabetes (7).

The abbreviation AABBCC is a handy mnemonic device for the components for a practical approach to diabetes classification that can help to differentiate between type 1 and type 2 diabetes (8). Its letters stand for:

• Age at diagnosis

• Autoimmunity (islet antibodies or other autoimmune diseases such as celiac disease, Crohn’s disease, thyroiditis, rheumatoid arthritis, Sjogren’s disease, and systemic lupus)

• Body habitus/BMI (particularly presentation with a BMI <27 kg/m²)

• Background (family history or membership in a high-risk population)

• Control (lack of glycemic control with worsening on noninsulin treatment)

• Comorbidities (particularly cardiovascular and renal conditions)

The diagnosis of type 1 diabetes in adults often is either not made correctly or delayed for many years. As primary care clinicians, we have the unique opportunity to make the correct diagnosis in a timely manner and then initiate appropriate therapy to improve both short- and long-term outcomes.