Type 1 diabetes defined by severe insulin deficiency occurs after 30 years of age and is commonly treated as type 2 diabetes.

This population-based cohort study sought to determine whether patients with adult-onset type 1 diabetes are misdiagnosed. Investigators found that 21% of the patients diagnosed with type 2 diabetes after age 30 actually had type 1 diabetes. They caution clinicians to carefully consider type 1 diabetes in adults requiring insulin.