More than a third of people over the age of 30 who are initially diagnosed with type 2 diabetes actually have type 1, meaning they are not receiving the right treatment, new research has revealed. The study, led by the University of Exeter, shows that 38% of patients with type 1 diabetes occurring after age 30 were initially treated as type 2 diabetes (without insulin). The team found that half of those misdiagnosed were still diagnosed as type 2 diabetes 13 years later.

The research, funded by NIHR and the Wellcome Trust, is published in the journal Diabetologia. The team analysed 583 people who had insulin-treated diabetes that had been diagnosed after the age of 30. The characteristics of their disease were compared with other participants who still produced some insulin, as well as with 220 individuals with severe insulin deficiency that was diagnosed before the age of 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.

The research shows that if a person diagnosed as type 2 diabetes needs insulin treatment within three years of diabetes diagnosis, they have a high chance of missed type 1 diabetes.

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