The University of Exeter study found a third of those they analysed were not given insulin, instead they received medication indicated for those with type 2 diabetes.
Further analysis found that half of those misdiagnosed were still being treated as though they have type 2 diabetes 13 years later.
Currently, guidance from the National Institute for Health and Care Excellence (NICE) for the diagnosis of diabetes does not recommend rigorous testing to differentiate between type 1 and type 2 in adults.
Lead researcher Dr Angus Jones, from the University of Exeter Medical School, said: “For people with type 1 diabetes, taking tablets and losing weight are not effective – they need insulin treatment.
“Our 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. Therefore, they need a blood test to confirm what type of diabetes they have, to ensure they receive the right monitoring, education and treatment.”
This study highlights how common misdiagnosing the type of diabetes in adults can be. One high-profile case saw Prime Minister Theresa May, misdiagnosed. She was given type 2 diabetes tablets and lifestyle advice which did not work, and it was only once she was re-tested that doctors discovered she actually had type 1 diabetes.
First study author Dr Nick Thomas, also from the University of Exeter Medical School, said: “While people with type 2 diabetes may eventually need insulin, their treatment and education is very different from type 1.
“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.”
A further problem with long-standing misdiagnosis is that consistently high glucose levels, from not having the right treatment, can greatly increase the risk of developing additional long-term complications such as amputation and heart, eye, kidney and nerve disease. These complications significantly impact upon quality of life as well as presenting significant cost for the NHS.
The research could prompt greater consideration of which type of diabetes is present following a diagnosis of diabetes. The study has been published in the Diabetologia journal.