Late-onset type 1 diabetes leading to severe endogenous insulin deficiency is common but often goes unrecognised, UK research suggests.

Endocrinologists found that one in five people diagnosed with insulin-treated diabetes over the age of 30 had almost absolute insulin deficiency, though many were managed as having type 2 diabetes.

In a paper published in Diabetologia they recommend that clinicians should suspect type 1 diabetes in an older patient who requires insulin within three years of diagnosis of diabetes.

The researchers from the University of Exeter Medical School reviewed the characteristics of 583 patients with insulin-treated diabetes diagnosed after age 30. They found that 21% had type 1 diabetes defined by the gold standard of rapid insulin requirement (within 3 years of diagnosis) and severe endogenous insulin deficiency (non-fasting C-peptide <200 pmol/l).

These patients had similar clinical, islet autoantibody and genetic characteristics to younger patients diagnosed with T1D. The study found that 38% of the patients with late onset T1D did not receive insulin at diagnosis, of whom almost half self-reported type 2 diabetes and 30% were treated with oral glucose-lowering therapy. Also, 47% of all those initially treated without insulin who progressed to insulin treatment within 3 years of diagnosis had severe endogenous insulin deficiency.

Rapid insulin requirement was highly predictive of severe endogenous insulin deficiency, with 85% of patients requiring insulin within one year of diagnosis.

The study authors said the difficulty in diagnosing T1D in later life had major clinical implications.

“Without a diagnosis of type 1 diabetes, a patient will not receive appropriate education and will not be eligible for interventions that are often restricted to those with type 1 diabetes, such as carbohydrate counting, continuous glucose monitoring and insulin-pump therapy. They will be at risk of ketoacidosis if insulin is withdrawn.”

“Clinicians should be aware that patients progressing to insulin within 3 years of diabetes diagnosis have a high likelihood of having type 1 diabetes, regardless of initial diagnosis,” they advised.