Percentile-based versus conventional thresholds in cardiopulmonary exercise testing: a retrospective cross-sectional study.

INTRODUCTION: Determining whether a value falls within the expected range is a central step in cardiopulmonary exercise testing (CPET) interpretation. Conventional thresholds based on absolute or percentage-predicted values are widely used but fail to capture population variability. This study evaluated the validity of percentile-based thresholds derived from the Study of Health in Pomerania (SHIP) for a Western population and compared their impact on classification with conventional thresholds in individuals without known cardiorespiratory disease and patients with cardiorespiratory disease. METHODS: We retrospectively analysed 886 maximal CPETs from 294 individuals without known cardiorespiratory disease (control group) and 592 patients with COPD, interstitial lung disease, heart failure or pulmonary hypertension. Percentile-based thresholds were evaluated for suitability by comparing abnormality rates with the expected 5% in the control group for peak oxygen uptake (V'O2 peak), ventilatory equivalent for carbon dioxide (V'E/V'CO2 nadir values), peak heart rate (HRpeak), V'O2 /work rate (WR) slope and peak V'O2 /HR. Agreement, discordance, and cumulative impact of percentile-based versus conventional thresholds were assessed. RESULTS: Percentile-based thresholds classified 4-8% of CPETs as abnormal in the control group, consistent with the expected 5%. In patients, conventional thresholds classified up to 14% more V'O2 peak values and 31% more HRpeak values as abnormal compared with percentile-based thresholds, whereas percentile-based thresholds identified more abnormal V'E/V'CO2 nadir values. Full agreement across all variables was observed in 82% of CPETs in the control group versus 46-58% in patients. CONCLUSION: The SHIP-derived percentile-based thresholds are valid for Western populations, and their application leads to substantial differences in abnormality classification of CPET results compared to conventional thresholds, especially in patients.