Type 1 diabetes defined by severe insulin deficiency


Posted Oct 17 , 2019 04:24 AM

Type 1 diabetes defined by severe insulin deficiency occurs after 30 years of age and is commonly treated as type 2 diabetes.
Diabetologia 2019_Online April 19

Institute Summary (excerpted from the abstract):

Late-onset type 1 diabetes can be difficult to identify. Measurement of endogenous insulin secretion using C peptide provides a gold standard classification of diabetes type in longstanding diabetes that closely relates to treatment requirements. The authors of the study set out to determine the prevalence and characteristics of type 1 diabetes defined by severe endogenous insulin deficiency after age 30 and assess whether these individuals are identified and managed as having type 1 diabetes in clinical practice. They assessed the characteristics of type 1 diabetes defined by rapid insulin requirement (within 3 years of diagnosis) and severe endogenous insulin deficiency (non-fasting C-peptide <200 pmol/l) in 583 participants with insulin-treated diabetes, diagnosed after age 30, from the Diabetes Alliance for Research in England (DARE) population cohort. They compared characteristics with participants with retained endogenous insulin secretion (non-fasting C-peptide >600 pmol/l) and 220 participants with severe insulin deficiency who were diagnosed under age 30. Twenty-one per cent of participants with insulin-treated diabetes who were diagnosed after age 30 met the study criteria for type 1 diabetes. Of these participants, 38% did not receive insulin at diagnosis, of whom 47% self-reported type 2 diabetes. Rapid insulin requirement was highly predictive of severe endogenous insulin deficiency: 85% required insulin within 1 year of diagnosis, and 47% of all those initially treated without insulin who progressed to insulin treatment within 3 years of diagnosis had severe endogenous insulin deficiency. Participants with late-onset type 1 diabetes defined by development of severe insulin deficiency had similar clinical characteristics to those with young-onset type 1 diabetes. However, those with later onset type 1 diabetes had a modestly lower type 1 diabetes genetic risk score, a higher islet autoantibody prevalence (GAD-, islet antigen 2 [IA2]- or zinc transporter protein 8 [ZnT8]- positive) of 78% at 13 years vs 62% at 26 years of diabetes duration, and were less likely to identify as having type 1 diabetes vs those with young-onset disease (79% vs 100%).

Why is this important?

It has been known for some time that the autoimmune processes associated with type 1 diabetes proceed with different intensities and different timelines. When we abandoned the use of the term ‘juvenile diabetes’ it was because not all patients developing type 1 diabetes were juveniles! Type 1 diabetes diagnosed over 30 years of age, defined by severe insulin deficiency, has similar clinical and biological characteristics to that occurring at younger ages but is frequently not identified and may be treated as type 2 diabetes. Clinicians should be aware that patients progressing to insulin within 3 years of diagnosis have a high likelihood of type 1 diabetes, regardless of initial diagnosis. In this study 21% of patients with severe insulin deficiency met the criteria for type 1 diabetes, and nearly half of these patients were diagnosed as having type 2 diabetes.

Concluding Thought: You won’t find what you don’t look for…

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