Double-checking C-peptide well after type 1 diagnosis can lead to reclassifications
medwireNews: Measuring C-peptide in everyone a minimum of 3 years after a clinical diagnosis of type 1 diabetes can result in some people being reclassified with other forms of diabetes, researchers report.
In 2017, the team from Western General Hospital in Edinburgh, UK, began testing all such patients, with 757 having been tested to date. Of these, 103 (13.7%) proved to have C-peptide levels of at least 200 pmol/L, and so underwent further investigation.
Overall, 27 were reclassified as having type 2 diabetes and eight with monogenic diabetes. Twelve patients stopped insulin as a result of their reassessment, and 32 are awaiting a final diagnosis.
The findings were presented at the Diabetes UK Professional Conference in Liverpool, UK, at which session co-Chair John Petrie (University of Glasgow, UK) commented: “The bottom line is that although for the majority of people this makes no difference, for a few people it makes a really big difference.”
Presenter Evgenia Foteinopoulou agreed, and noted that the approach is cost effective. She also stressed that 5.7% of patients with confirmed type 1 diabetes nevertheless had C-peptide levels greater than 200 pmol/L, so this finding alone does not warrant a change of diagnosis.
People who were older than 35 years at type 1 diabetes diagnosis were the most likely to be reclassified. About half of these people were reclassified to type 2 diabetes, although some proved to have a monogenic form.
In response to an audience question, from Stephanie Amiel (King’s College, London, UK), Foteinopoulou conceded that the type 2 diabetes diagnoses were based largely on clinical judgement, but stressed that they considered a bigger picture than just glucose and C-peptide levels, including BMI, family history, and negative autoantibodies, in addition to which some patients had screened negative for monogenic diabetes.
Just over two-thirds (67.9%) of the cohort had C-peptide levels of 200–600 pmol/L, 18.4% had levels of 600–900 pmol/L, and 13.5% had levels exceeding 900 pmol/L.
Thirteen of the 14 patients with levels exceeding 900 pmol/L have been reclassified as having type 2 diabetes, with one currently undergoing genetic testing, reported Foteinopoulou. But she noted that four patients no longer considered to have type 1 diabetes had diabetic ketoacidosis at diagnosis.
Of the 19 patients with levels of 600–900 pmol/L, eight were positive for autoantibodies and considered to have type 1 diabetes, yet one was nonetheless able to discontinue insulin after 6 years of use. The 11 who were negative for autoantibodies included five who were reclassified as having type 2 diabetes, one with confirmed maturity onset diabetes of the young (MODY), and one with maternally inherited diabetes and deafness.
Seventy patients had C-peptide levels of 200–600 pmol/L and included 39 with positive autoantibodies, two of whom also had MODY mutations. A further 24 were negative for autoantibodies, including nine who were reclassified as having type 2 diabetes, three who had MODY mutations, and one who had maternally inherited diabetes and deafness.
“We strongly believe that all people with a clinical diagnosis of type 1 diabetes should have a one-off measurement of C-peptide after 3 years,” concluded Foteinopoulou.
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