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Diabetes diagnosis improved by quick, inexpensive C-peptide test

While supported by an NIHR Clinician Scientist award, Professor Angus Jones and his colleagues developed convenient blood and urine C-peptide tests to confirm patients’ diabetes diagnosis.

Published: 27 October 2023

Developing solutions to diagnostic problems in diabetes

Over 4 million people in the UK have been diagnosed with diabetes and, by 2035, cases are predicted to reach 6.25 million. As diabetes can lead to numerous health complications, improving its treatment and prevention is considered a national clinical priority in the NHS Long Term Plan.

Professor Angus Jones has received 4 career development awards from the NIHR to support his research towards improving the diagnosis of diabetes as well as his career development as a researcher.

C-peptide: a quick and cheap test to check the diagnosis

Nine out of 10 cases are diagnosed as type 2 diabetes, but it can be hard to differentiate this from type 1 or other rare forms of the condition. Professor Jones, Associate Professor at NIHR Exeter Clinical Research Facility, explained: “Up to 15% of insulin-treated patients are misdiagnosed. This figure soars to 40% among people who develop type 1 diabetes after the age of 30.”

"Treatment for type 1 and type 2 diabetes is very different, which is why being able to confirm that a person has the right diagnosis is so important”.

Professor Angus Jones

Professor Jones’ NIHR-funded project has transformed the accuracy of diabetes diagnosis through the development of a quick, inexpensive C-peptide test to measure insulin levels in the blood or urine.

Working alongside NIHR-funded researchers Dr Tim McDonald and Professor Andrew Hattersley, their £10 test can identify whether a person should be treated and monitored as having either type 1 or 2 diabetes. This may mean stopping unnecessary insulin therapy, which greatly improves a patient’s quality of life and makes significant cost savings for the NHS.

Recommendations from their work have influenced numerous C-peptide guidelines, including those developed by NICE, the Association of British Clinical Diabetologists and the International Society of Pediatric and Adolescent Diabetes.

In practice, 7 NHS specialist clinical laboratories in the UK now offer the new urine test, with Dr McDonald’s Exeter laboratory receiving over 8,000 NHS referrals annually. C-peptide testing is offered routinely to all patients diagnosed with type 1 diabetes in Scotland.

Making the right diagnosis when people first develop diabetes

C-peptide testing is most useful at least 3 years after a patient’s diabetes diagnosis, so the initial diagnosis can still be uncertain. With NIHR’s support, Professor Jones developed a model that predicts when someone with diabetes will stop making their own insulin.

The NIHR Clinical Research Network then helped to recruit over 1,800 patients with newly diagnosed diabetes to test whether the model can improve patients’ early care. The final model will be freely available to health professionals through a website and smartphone app, helping to improve patient experience, health outcomes and cut NHS costs.

Professor Jones’s NIHR-funded work also contributed to a major recent change to international and NICE diabetes guidelines, which recommend that everyone with suspected type 1 diabetes is tested for islet autoantibodies. This helps to confirm their diagnosis as well as identify whether someone has been misdiagnosed.

“By getting the diagnosis right using tests like C-peptide, or our newly developed prediction models, we can make sure patients have the right diagnosis and therefore receive the best treatment.”

Professor Angus Jones

During his NIHR-funded doctoral research fellowship, Professor Jones investigated the best treatment for patients with type 2 diabetes. Published in the journal Diabetes Care, the study of more than 950 people confirmed that C-peptide testing identified patients who wouldn’t benefit from costly glucose-lowering treatments.

The team also developed models to help health professionals choose the best medication for their individual patients. With NIHR funding, they are developing these models for use in clinical practice, helping to ensure patients receive the most effective treatments.

Reflecting on his career to date, Professor Jones said: “Without a doubt I would not be a clinical academic today without the support and opportunities I have had from NIHR”.

“NIHR’s support has allowed me to develop my research interests and a clinical academic career, as well as contribute to a programme of research that has helped change approaches to classification and management of diabetes internationally.”

Professor Angus Jones

More information about the studies is available on the NIHR’s Funding & Awards website.

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