INS and Impaired glucose tolerance: Even patients with CF who had normal glucose tolerance (NGT) were found to have deficient insulin secretion in the study.319 In a two-year follow-up of patients with CF, CF patients preferentially exhibit impaired first-phase insulin secretion, with insulin output showing a decreasing effect over time in both oral and intravenous glucose tolerance tests.320,321 The progression of CFRD can progress sequentially through glycemic uncertainty, impaired glucose tolerance, CFRD without high fasting glucose, and CFRD with high fasting glucose.