insulin pump

Many people with type 1 diabetes continue to secrete small amounts of insulin long after diagnosis, particularly those who develop the condition in adolescence or adulthood.

That was the finding of two studies published online December 17, 2014 in Diabetes Care. One study, led by Dr Asa K Davis (Benaroya Research Institute, Seattle, Washington) and colleagues, found that residual insulin secretion was present in one of three people diagnosed with type 1 diabetes 3 years or more earlier.

In the other study, by Dr Richard A Oram (National Institute for Health Research, University of Exeter Medical School, UK), 80% of patients aged less than 30 years when diagnosed with type 1 diabetes and a disease duration of 5 years or longer still had detectable C-peptide levels.

“The old dictum is that if you have type 1 diabetes long enough you don’t have any C-peptide, yet if you have a sensitive enough assay, many people do,” Dr Anne L Peters (Keck School of Medicine, University of Southern California, Los Angeles, California) told Medscape Medical News.

The finding, which has been previously reported but not in large studies — each of these new studies involved more than 900 patients — suggests that one day it may be possible to recover and reharness beta-cell production. But the finding also has immediate clinical relevance, particularly with regard to diagnosing type 1 diabetes, according to Dr Peters, a coauthor of the first study.

“People with type 1 diabetes still have beta cells and still make some insulin because the autoimmune process may not cause complete beta-cell destruction. It’s interesting and confuses the diagnosis, but doesn’t take away that this is an autoimmune disease,”

Importantly, the study she was involved with showed that C-peptide levels tend to be higher among people who develop type 1 diabetes in adulthood, a scenario that may be unfamiliar to many clinicians who trained in the era when type 1 diabetes was called juvenile diabetes. Indeed, Dr Peters often sees patients with adult-onset autoimmune diabetes who had been misdiagnosed with type 2 diabetes and inappropriately prescribed metformin instead of insulin.

“People need to know that autoimmune type 1 diabetes can occur at any age and that older-onset type 1 patients retain the ability to make C-peptide longer than those who get it younger. This is not the cut-and-dried C-peptide-negative and -positive story we once thought….Think of type 1 in adults who don’t fit the typical type2 picture, and if you’re confused send the patient to an endocrinologist, because this isn’t simple,” she advised.

Microsecretors Common

Davis and colleagues measured C-peptide levels in 919 patients at 28 sites participating in the T1D Exchange Clinic Network. Patients were aged 6 months to 46 years (median, 14 years) when they were diagnosed with autoimmune type 1 diabetes and had a disease duration of at least 3 years (median, 13 years).

Overall, 29% had detectable non fasting C-peptide levels of 0.017 nmol/L or greater, and 10% had levels of 0.2 nmol/L or greater.

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