C-Peptide Test Helps Diagnose and Treat Diabetes Accurately

C-peptide levels in the blood or urine can indicate how much insulin is being produced and therefore, can be used as a simple and cheap test to diagnose the type of diabetes that a patient has. This can help doctors to change the medications accordingly. A team of researchers at the University of Exeter Medical School, UK have developed one such test, which is being presented at the Diabetes UK Professional Conference 2019 at the Arena and Convention Center (ACC), Liverpool, UK.

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C-Peptide and its Role in Diagnosis of Diabetes

C-peptide, also known as a connecting peptide, is a short 31-amino acid polypeptide that connects insulin’s A-chain with its B-chain in the proinsulin molecule. A C-peptide test is used to differentiate between Type-1 and Type-2 diabetes. In Type-1 diabetes, very little or no insulin is produced, and so, the corresponding C-peptide level is also very low. In Type-2 diabetes, however, an ample amount of insulin is produced, and therefore, the level of C-peptide is much more elevated and higher than normal values. This difference in the levels of C-peptide helps to diagnose and differentiate between Type-1 and Type-2 diabetes more accurately.

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The C-Peptide Test Developed by the University of Exeter, UK

A team of researchers at the University of Exeter Medical School, UK have developed a simple and inexpensive test for measuring the levels of C-peptide in the blood or urine, which can show what kind of treatment will be most effective in diabetic patients. The test has been evaluated by clinicians at the Western General Hospital in Edinburgh, Scotland in over 750 patients, clinically diagnosed as having Type-1 diabetes for over three years.

The C-peptide test results revealed that these patients were not actually Type-1 diabetics and therefore, the insulin therapy could be stopped and oral tablets could be given instead. In fact, Type-2 diabetes was clinically misdiagnosed as Type-1 diabetes in 28 patients and in 12 patients; it was actually possible to stop the insulin therapy.

In this regard, Dr. Angus Jones, from the University of Exeter Medical School, says: "It can be highly challenging for clinicians to differentiate between Type-1 and Type-2, and a number of genetic subtypes of diabetes. Up to 15 percent of insulin treated patients are misdiagnosed. This figure soars to 40 percent of people developing Type-1 diabetes after age 30, as identifying Type-1 diabetes at this age is very difficult. Treatment for these is very different, which is why being able to confirm if a person has the right diagnosis is so important. For example, people with Type-1 diabetes need lifelong insulin injections and become very unwell without this treatment, but most people with Type-2 and genetic subtypes of diabetes can be effectively treated with tablets. By measuring C-peptide in a person receiving insulin treatment, we can make sure they have the right diagnosis, and therefore the best treatment for them."

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Salient Features of the New C-Peptide Test

• It is simple, robust and cheap – costing just £10 per test
• It has an impact on deciding the correct treatment, patient education and follow-up care
• It can reveal if there is a genetic cause behind diabetes, which impacts treatment as well as establishing whether there is a family history of the disease. A genetic cause has been confirmed in 8 patients
• Measuring C-peptide levels can tell how much insulin is being produced de novo within the body, even if the patient is taking insulin injections
• The test is available in Edinburgh and Glasgow under the National Health Service (NHS) for testing patients with Type-1 diabetes for at least three years

Study Findings

• Optimal storage conditions for the blood and urine samples were established, making sample collection and storage easier
• A specific preservative was identified that allowed blood C-peptide samples to be stored for over 24 hours
• The above findings permit C-peptide testing to be used in routine clinical care in outpatient clinics
• Blood and urine C-peptide testing can identify the correct subtype of diabetes
• C-peptide is a cheap and effective test for diagnosing a genetic form of diabetes, which otherwise requires expensive tests
• Clinical studies show that C-peptide can predict the efficacy of specific antidiabetic drugs in individual patients
• C-peptide can stratify response to a costly therapy in diabetics on insulin, thereby identifying patients unlikely to benefit from the therapy
• Low C-peptide is associated with higher fluctuations in blood glucose, thereby increasing the risk of hypoglycemia in Type-2 diabetics on insulin

Expert Comments

Dr. Tim McDonald, of the University of Exeter Medical School, says: “Getting the right diagnosis in diabetes is absolutely key to achieving the best treatment outcomes and avoiding complications. We’ve shown that C-peptide is cheaper, more accurate and easier to use than previous methods. It’s really gratifying to see this making a difference to improving patient health already. My lab alone has received 7,000 test samples in the past 12 months.”

Dr. Emily Burns, who is Head of Research Communications at Diabetes UK, says: “Getting the right diagnosis of diabetes is so important; it means people will receive the right treatment for them and could avoid serious complications. But different forms of diabetes can be difficult to accurately diagnose. Researchers at the University of Exeter are leading the way in improving how we diagnose diabetes, and in making tests more widely available, to make sure as many people as possible can benefit.”

Conclusion

The C-peptide test in Type-1 diabetes patients can improve diagnostic accuracy. It may even permit stopping of insulin therapy in some patients if the test results indicate Type-2 rather than Type-1 diabetes.

Reference:

1. Measurement of C‐peptide in Patients with a Clinical Diagnosis of Type 1 Diabetes Improves Diagnostic Accuracy and May Allow Cessation of Insulin Therapy in Some Individuals [Abstract: A8 (P97)] - (https://doi.org/10.1111/dme.1_13882)

Source-Medindia