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Feature Endocrinology

The wrong diabetes: how C peptide testing might help

BMJ 2019; 365 doi: (Published 25 June 2019) Cite this as: BMJ 2019;365:l4352
  1. Jacqui Wise, freelance journalist
  1. London, UK
  1. jacquiyoung1{at}

A single misdiagnosed patient was the catalyst for offering C peptide testing to all patients with type 1 diabetes in the Lothian region, writes Jacqui Wise. This simple test can help patients get the correct diabetes diagnosis

Sophie Fleming was diagnosed as having type 1 diabetes mellitus when she was 8 years old and was treated with insulin for 27 years. Her diagnosis, however, was wrong.

This was discovered by chance in 2016. Her father had been diagnosed with type 2 diabetes, but a genetic test found that he actually had a form of monogenic diabetes (also known as maturity onset diabetes of the young, or MODY), a rare form of diabetes caused by a mutation in a single gene.

Fleming was subsequently tested: she had inherited the same genetic variant. A test for C peptide showed that she was producing some insulin, which meant that her diabetes could be well controlled with sulfonylurea tablets, which preclude the need for glucose monitoring.

“It’s been life changing. I thought I would be on insulin for the rest of my life,” she says.

Insulin can cause weight gain and hypoglycaemia, and taking it is restrictive and inconvenient for patients. They may have to wear an insulin pump 24 hours a day and take multiple blood tests.

“I’m looking forward to being able to go to a water park,” says Fleming. “And going on holiday is much easier now, for example, packing and getting through airport security.”

On our radar

Mark Strachan, consultant in diabetes and endocrinology at the Western General Hospital in Edinburgh, tells The BMJ, “We have a large clinic of people with monogenic diabetes, and …

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