What characterizes type 1 diabetes mellitus?

Type 1 diabetes mellitus is characterized by the absolute absence of insulin production due to autoimmune destruction of the pancreatic beta cells, which are responsible for producing insulin. This form of diabetes typically presents in younger individuals, often in childhood or adolescence, though it can occur at any age. Because the body is unable to produce insulin, patients rely on external sources of insulin to regulate their blood sugar levels.

In contrast to type 1 diabetes, type 2 diabetes is more often associated with insulin resistance, where the body's cells do not respond effectively to insulin. Additionally, excessive insulin production is not a feature of type 1 diabetes; in fact, insulin levels can be low or undetectable in these patients. While high glucagon levels may be present due to dysregulation of glucose metabolism in diabetes, the defining characteristic of type 1 diabetes is the lack of insulin secretion from the pancreas.