Background While exercise testing is increasingly used as a prognostic indicator in cystic fibrosis (CF), it is reported to be underused in UK CF centres, particularly in children. Here, we evaluated the cardiopulmonary exercise testing (CPET) results in children and young people with CF at CF annual review and its possible clinical value.

Method An observational study comparing CPET results using a cycle ergometer ramp test (peak oxygen uptake (Vo_2peak)) and pulmonary function (forced expiratory volume in 1 s (FEV₁)) was performed with body mass index (BMI) used as a disease severity marker. Data were identified from clinical case notes and our CF database.

Results Thirty-eight children and young people (mean age 11±2.4, range 7–14 years; 17 males and 21 females) completed at least one CPET with 95% achieving technically satisfactory tests allowing measurement of Vo_2peak. Mean Vo_2peak was 107 ±17.6% predicted, range 74%–150% predicted, with 8% having a reduced Vo_2peak of <85% of predicted. Mean FEV₁ z-score was −0.77±1.24, range −4.42 to 2.24. We did not demonstrate a significant correlation between Vo_2peak % predicted and FEV₁ z-score (r=0.25, p=0.13), or between Vo_2peak % predicted and BMI z-score (r=−0.05, p=0.77). Twenty-eight of 38 completed a second CPET the following year with 71% showing a decline in Vo_2peak (mean decline of 8% of predicted value, equivalent to 3.8 mL/kg/min).

Conclusion CPET is feasible with 95% of children and young people achieving technically satisfactory assessments starting from age 7. In this group with relatively mild CF, mean Vo_2peak was normal with no significant correlation between Vo_2peak and FEV₁ or BMI, as markers of disease severity. The majority demonstrated a normal Vo_2peak. However, 71% showed a downward trend on repeat testing 12–18 months later.