Abstract

Objective: Progressive Beta-cell loss causes catabolism in Cystic Fibrosis (CF). Existing diagnostic criteria for diabetes were based on microvascular complications rather than CF-specific outcomes.

We aimed to relate glycemic status in CF to weight and lung-function changes.

Research Design and Methods: We determined peak blood glucose (BG_max) during Oral Glucose Tolerance Tests (OGTT) with samples every 30 minutes on 33 consecutive children (aged 10.2–18 years). Twenty-five also agreed to Continuous Glucose Monitoring (CGM, Medtronic).

Outcome Measures were change in weight Standard Deviation Score (wtSDS), %Forced Expiratory Volume in 1 second (%FEV1), and %Forced Vital Capacity (%FVC) in the year preceding OGTT.

Results: Declining wtSDS and %FVC were associated with higher BG_max (both p=0.02) and with CGM-time above 7.8mmol/l (p=0.006 and p=0.02 respectively), but not with BG_120mins. Decline in %FEV1 was related to CGM-time above 7.8mmol/l (p=0.02). Using Receiver Operating Characteristic (ROC) analysis to determine optimal glycemic cut-offs, CGM-time above 7.8mmol/l ≥4.5% detected declining wtSDS with 89% sensitivity and 86% specificity (AUC 0.89, p=0.003). BG_max ≥8.2 mmol/l gave 87% sensitivity and 70% specificity (AUC 0.76, p=0.02). BG_120mins did not detect declining wtSDS (AUC 0.59, p=0.41). After excluding 2 patients with BG_120mins ≥11.1 mmol/L, decline in wtSDS was worse if peak BG was ≥8.2mmol/l (−0.3±0.4 vs 0.0±0.4 for BG <8.2, p=0.04) or if CGM-time above 7.8mmol/l was ≥4.5% (−0.3±0.4 vs +0.1±0.2 for time <4.5%, p=0.01).

Conclusions: BG_max on OGTT ≥ 8.2 mmol/L and CGM-time above 7.8mmol/l ≥4.5% are associated with declining wtSDS and lung-function in the preceding 12 months.