Prevalence of hypoglycemia during oral glucose tolerance testing in adults with cystic fibrosis and risk of developing cystic fibrosis-related diabetes.

Background: Hypoglycemia in cystic fibrosis (CF) patients during the oral glucose tolerance test (OGTT) has been reported; however, these patients have not been well-characterized. Few studies have examined whether hypoglycemia during the OGTT increases the risk of developing CF-related diabetes (CFRD). Objectives of this study were to describe the characteristics of CF patients with hypoglycemia during the OGTT and to determine the incidence and time to development of CFRD in those with hypoglycemia.

Methods: This cohort study included 466 adults with CF at the Toronto Adult CF Clinic between 1996 and 2015. Subjects were classified into two groups based on their plasma glucose (PG) level 2 h after a 75 g OGTT: hypoglycemia (PG ≤ 3.9 mmol/L) or no hypoglycemia (PG > 3.9 mmol/L). Clinical and demographic data were collected from the clinic visit closest to the OGTT. Differences between groups were assessed using Fisher's exact test or Mann-Whitney-Wilcoxon test.

Results: 138 patients (29.6%) experienced hypoglycemia during the OGTT. More males experienced hypoglycemia compared to no hypoglycemia (69.6% vs. 54.6% respectively; p = 0.003). Those who were heterozygous deltaF508 were more likely to experience hypoglycemia (p = 0.006). Subjects who experienced hypoglycemia were less likely to develop CFRD at ten years compared to no hypoglycemia (12.0% vs. 42.1%, respectively; p < 0.001).

Conclusions: Hypoglycemia following OGTT is common in CF however the 10 year risk of developing CFRD in these patients was low. Males and those who were heterozygous deltaF508 were at higher risk for hypoglycemia.