β-Cell secretory defects are present in pancreatic insufficient cystic fibrosis with 1-hour oral glucose tolerance test glucose ≥155 mg/dL.

PI-CF patients with 1-hour OGTT glucose ≥155 mg/dL already manifest impaired β-cell secretory capacity with associated early-phase insulin secretion defects. Avoiding hyperglycemia in patients with EGI may be important for preventing excessive insulin demand indicated by disproportionately increased proinsulin secretion.