Validation of insulin secretion indices in cystic fibrosis patients

Impaired insulin secretion plays a key role in the development of cystic fibrosis-related diabetes (CFDR). Numerous indices to evaluate insulin secretion have been proposed, but their validity has not been explored in cystic fibrosis (CF). The aim of the present study was to validate surrogate indices of insulin secretion in CF patients against the gold standard, the intravenous glucose tolerance test (IVGTT).

32 subjects were enrolled: 16 controls, 10 cystic fibrosis-normal glucose tolerant (CF-NGT) and 6 CFRD patients. All subjects underwent a 2-h oral glucose tolerance test (OGTT) and an IVGTT. Insulin secretion was estimated using three indices: the HOMA-beta cell, the Stumvoll's early insulin secretion, and the insulin secretion rate (ISR).

In control subjects, all insulin secretion indices correlated significantly with the IVGTT. In CF-NGT patients, the HOMA-beta cell correlated significantly with the IVGTT at shorter time points but not over longer time-period. On the other hand, both OGTT-derived indices (Stumvoll and IRS) correlated significantly with the IVGTT for the CF-NGT and CFRD groups.

Since the OGTT is required on a regular basis in CF patients to screen for CFRD, OGTT-derived indices appear to be suitable for evaluating insulin secretion.