Of all diabetics, about 90% are T2. The classification of T1D and T2D isn’t always clear. Both conditions are the result of various genetic and environmental factors that cause progressive loss of beta-cell mass and/or function that manifests as hyperglycemia.[1]
Unlike T2D, T1D is an autoimmune condition. Additionally, T1D is characterized by insulin deficiency, whereas T2D is characterized by insulin resistance and inadequate insulin secretion.
People with T1D are more often diagnosed at a younger age (< 30 years); have a lower BMI (< 25); report unintentional weight loss, polyuria (excessive urination), and polydipsia (excessive thirst); and almost half present with diabetic ketoacidosis.[2]. The risk of developing T1 diabetes is not strongly affected by lifestyle factors whereas risk of T2D is.
However, there are exceptions to these generalities. A number of adults aged > 30 years diagnosed with T2D actually have T1D (known as “latent autoimmune diabetes of adults”) and some children and adolescents are diagnosed with T2D (known as “maturity-onset diabetes of the young”). Also, patients with T2D occasionally present with diabetic ketoacidosis.
A relatively reliable way to differentiate between T1D and T2D is to test for the presence of islet autoantibodies in the blood.