1ST-PHASE INSULIN-RESPONSE TO INTRAVENOUS GLUCOSE IN CYSTIC-FIBROSIS PATIENTS WITH DIFFERENT DEGREES OF GLUCOSE-TOLERANCE

The aim of our study was to determine whether first-phase insulin resp onse to intravenous (i.v.) glucose could be used as a simple and rapid test to identify cystic fibrosis (CF) patients at risk to develop dia betes mellitus. Forty consecutive CF patients with normal fasting bloo d glucose values but with different degrees of glucose tolerance on th e standard oral glucose tolerance test (22 with normal glucose toleran ce, 16 with impaired glucose tolerance, 2 with diabetes mellitus) and 12 normal subjects, matched for age and body mass index, underwent an i.v. glucose bolus to evaluate early phase insulin release. When compa red to the normal subjects, CF patients had significantly reduced basa l (76 +/- 50 vs 108 +/- 30 pM/l, 2p<0.02) and glucose stimulated insul in levels (1+3 min insulin=456 +/- 275 vs 951 +/- 170 pM/l, 2p<0.01). Early phase insulin release, however, did not differentiate between CF patients with normal and impaired glucose tolerance; also in the two diabetic patients insulin levels did not clearly differ from those obs erved in the other groups of CF subjects. In conclusion, first-phase i nsulin response may identify an impairment of B-cell function in CF su bjects; however, it does not discriminate between different degrees of glucose tolerance, as determined by the oral glucose tolerance test a nd, therefore, it does not reliably identify those patients who will e ventually develop overt diabetes mellitus.