One-Third of Type 1 Diabetes Cases Misdiagnosed in Those Over Age 30


Older patients who are improperly diagnosed may not gain access to insulin and delivery and monitoring tools, such as pumps or continuous glucose monitoring.

New research from the United Kingdom finds that one-third of those who develop type 1 diabetes (T1D) after age 30 are initially misdiagnosed and treated for type 2 diabetes (T2D), without insulin.

The study appearing in Diabetologia, calls attention to the difficulty of correctly diagnosing older patients with T1D, which may look very similar to T2D. Measuring endogenous insulin secretion using C-peptide offers the gold standard for classifying diabetes by type.

“For people with type 1 diabetes, taking tablets and losing weight are not effective—they need insulin treatment,” study leader Angus Jones, MBBS, PhD, of the University of Exeter, said in a statement. “It is very difficult to diagnose type 1 diabetes in older adults, as most people this age will have type 2, even if they are thin. Our research shows that if a person diagnosed with type 2 needs insulin treatment within 3 years of diabetes diagnosis, they have a high chance of missed type 1 diabetes. Therefore, they need a blood test to confirm what type of diabetes they have, to ensure they receive the right monitoring, education, and treatment."

Patients who are improperly diagnosed may not gain access to the right treatments, including insulin, as the need for both insulin and delivery and monitoring systems, such as pumps or continuous glucose monitoring (CGM) systems, rapidly increases over the first year of diagnosis, the study authors wrote. Many payers will not cover CGM in for people with T2D.

Researchers examined characteristics of 583 patients who had insulin-treated diabetes that was diagnosed after age 30. These patients needed insulin within 3 years of diagnosis and had severe endogenous insulin deficiency, with nonfasting C-peptide <200 pmol/L. The research team compared the characteristics of these patients who retained endogenous insulin secretion (>600 pmol/L) and 220 patients with severe insulin deficiency who were diagnosed before turning 30.

The study found the following:

  • 21% of those with insulin-treated diabetes diagnosed after age 30 met the study criteria for T1D. Of these 38% did not receive insulin when first diagnosed, of whom 47% said they were diagnosed with T2D.
  • The need for insulin soon after diagnosis was highly predictive of severe endogenous deficiency; 85% needed insulin within 1 year of diagnosis, and 47% of all patients who were not treated with insulin at diagnosis but needed it within 3 years had severe endogenous deficiency.
  • While those with late-onset T1D had similar characteristics to those with young-onset T1D, the later onset patients had genetic risk scores that were “modestly lower” than younger onset patients, higher islet autoantibody prevalence, and were less likely to identify has having T1D.

“While people with type 2 diabetes may eventually need insulin, their treatment and education is very different from type 1," said Nick Thomas, lead author and also from University of Exeter. "If people with type 1 diabetes don’t receive insulin they can develop very high blood glucose, and may develop a life-threatening condition called ketoacidosis. This means having the right diagnosis is vitally important even if insulin treatment has already been started."


Thomas NJ, Lynam AL, Hill AV, et al. Type 1 diabetes defined by severe insulin deficiency occurs after 30 years of age and is commonly treated as type 2 diabetes [published online April 30, 2019]. Diabetologia. 2019; doi:10.1007/s00125-019-4863-8.

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