People with cystic fibrosis-related diabetes (CFRD) are known to have reduced exercise capacity (EC), which in turn is related to increased morbidity and mortality. The aim of this study was to examine whether dysglycaemia may independently influence exercise capacity in people with CF (pwCF).

Results from clinically conducted cardiopulmonary exercise tests were analysed retrospectively in 139 pwCF alongside routine clinical data. Subjects were grouped according to glycaemic status; normal glucose tolerance (NGT; n = 43) and dysglycaemia; impaired glucose tolerance (IGT; n = 17) and CFRD (n = 79). Anthropometric data was assessed using chi-squared tests. Regression models were developed using analysis of co-variance (ANCOVA) to evaluate predictors of exercise capacity and correlations between variable were assessed using the Pearson method.

Maximal oxygen uptake (VO_2max) was reduced in the CFRD group compared to NGT and IGT (p < 0.01), however this was dependent on higher FEV₁ % in the NGT and IGT groups (p < 0.001) and significant differences were no longer present when FEV₁ was accounted for. A higher proportion of those with dysglycaemia were ventilatory limited (NGT; 42 %, IGT; 72 % & CFRD; 65 %, p < 0.05). Age, gender, BMI, intravenous antibiotic days and FEV₁ % were significant predictors of VO_2max across all patients (adjusted R² = 0.528, p < 0.001). HbA1_c is a small but significant predictor of VO_2max in patients with dysglycaemia (p < 0.05).

Adults with CFRD have reduced VO_2max compared to NGT or IGT which is mediated by poorer lung function and higher overall disease burden. In individuals with CFRD, better glycaemic control is associated with a greater EC.