Association of islet amyloid polypeptide to C-peptide ratio with cystic fibrosis-related diabetes: a prospective cross-sectional study

Objectives: Early detection of cystic fibrosis (CF) related diabetes (CFRD) improves health outcomes and reduces CF-related mortality. The study aims to evaluate the ratio of islet amyloid polypeptide (IAPP) to C-peptide in CF patients with diabetes and without diabetes. Methods: Cross-sectional analysis was carried out in a prospective cohort of 33 participants (CF [n=16] and CFRD [n=18]). We examined the association of plasma IAPP:C-peptide ratio with clinical information, including glycated hemoglobin, and lung function markers. Results: The median (interquartile range) IAPP:C-peptide ratio was significantly (P=0.004) higher in people with CFRD (4.8 [4.5]) compared with participants without CFRD (12.1 [19.7]). The ratio of IAPP to C-peptide significantly accounted for a 38% variation in the diabetes status in patients with CF (r²=0.399, P < 0.001). Islet amyloid polypeptide is strongly correlated with serum ferritin levels (r=0.683, P=0.005) and forced expiratory volume in CFRD, but not in nondiabetic participants with CF. Conclusions: Islet amyloid polypeptide:C-peptide ratio could be a potential marker of CFRD in adults with CF. Further research requires validation of this marker in longitudinal cohort studies to confirm the capability of IAPP:C-peptide to predict CFRD.