Endocrine Abstracts

C-peptide is a marker of pancreatic beta cell function and is used to investigate hypoglycaemic disorders and aid diabetes classification. An international consensus report (ADA/EASD) on the management of type 1 diabetes recommends C-peptide (with concurrent glucose) measurement, in individuals 3 years after diagnosis where there is uncertainty about diabetes classification. We conducted a retrospective audit of C-peptide testing among adult patients in Galway University Hospitals. All relevant laboratory data for the calendar year 2023 were retrieved from the laboratory information system. Patient demographic and clinical data were retrieved from electronic medical records. 192 tests were undertaken on 181 adults with C-peptide results ranging 7-4199 pmol/l (ref. interval 370-1470 pmol/l) with a median of 754 pmol/l (IQR 404-1230 pmol/l). 18 patients had a C-peptide level <200 pmol/l; one was undertaken due to hypoglycaemia, 4 were conducted at the time of diagnosis and 13 patients were already on insulin therapy. Only 56% of samples had a concurrent glucose measurement to facilitate interpretation. 124 patients had a diagnosis of diabetes at the time of testing with 30 of these being a new diagnosis. The most common indication for testing was to determine diabetes classification (n = 83), only 28 took place a minimum of 3 years post-diagnosis, followed by hypoglycaemia workup (n = 26) and assessment of endogenous insulin production (n = 25). 92 samples were paired with islet autoantibody testing. Based on a combination of islet autoantibody and C-peptide results 15 patients (8.2%) had a diabetes reclassification. Appropriate use of C-peptide measurement can aid better diabetes classification with implications for patient self-management, education and risk counselling. Our findings highlight the importance of C-peptide as a diagnostic aid for classifying diabetes and calls for closer adherence to recommended guidelines for testing.