ABSTRACT
AIM: Cystic fibrosis-related diabetes (CFRD) prevalence has increased dramatically with the improved life expectancy of patients with cystic fibrosis (CF). Glycated haemoglobin (HbA(1c)) is an important tool for monitoring blood glucose control but, unlike in type 1 and type 2 diabetes, a correlation between HbA(1c), fructosamine and mean plasma glucose has not been clearly established in CF. This study aimed to examine the relationship between mean plasma glucose and HbA(1c) or fructosamine in stable patients with CFRD. METHODS: Fifteen type 1 diabetes and 13 CFRD patients (HbA(1c)<9.0%; no anaemia), matched for age and body mass index (BMI), provided 72 capillary blood glucose profiles taken 3days/month for three months. At the end of this time, HbA(1c) and fructosamine were measured. Mean plasma glucose was estimated using the Diabetes Control and Complications Trial (DCCT) conversion formula, and linear regressions carried out to establish its relationship with HbA(1c) and fructosamine. RESULTS: In type 1 diabetes patients, mean plasma glucose correlated significantly with HbA(1c) (r=0.68; P=0.005). In CFRD patients, no correlation was found between mean plasma glucose and HbA(1c) (r=0.24; P=0.460). Also, no association was found between mean plasma glucose, representing the month before blood sampling, and fructosamine in either group. CONCLUSION: Unlike in type 1 diabetes, HbA(1c) did not correlate with mean plasma glucose in CFRD subjects. Thus, having a normal HbA(1c) may not be sufficient to indicate a low risk of diabetes complications in CFRD. Further studies are required to explain such a discrepancy.