Objectives Patient-relevant measures of functional status are required in chronic obstructive pulmonary disease (COPD) and lung cancer in clinical practice and research. We explored the relationship between the Australia-modified Karnofsky Performance Scale (AKPS) and measures of functional capacity and physical activity in these patient groups.

Methods Pooled clinical trial data were analysed to explore the relationship between AKPS and average daily steps (ADS), 6 min walk distance (6MWD), and body mass index, airflow obstruction, dyspnoea and exercise score (COPD group). Receiver operator characteristic curves were produced to compare sensitivity and specificity of cut-offs (no dependency >70, high dependency <60) and area under the curve (AUC).

Results Seven clinical trials included people with COPD (n=79) and lung cancer (n=150). To detect an AKPS of >70, the optimal ADS cut-points were COPD, 3342 steps (AUC 0.88, 95% CI 0.79 to 0.97, sensitivity 82%, specificity 76%), and lung cancer, 3380 steps (AUC 0.72, 95% CI 0.64 to 0.81, sensitivity 61%, specificity 74%), and for 6MWD (COPD only) 242 m (AUC 0.72, 95% CI 0.63 to 0.81, sensitivity 73%, specificity 34%).

Conclusions An AKPS score is strongly related to ADS in people with COPD and lung cancer. The AKPS may be useful in clinical practice and research to indicate levels of physical activity where ADS and 6 min walk test are not possible. Longitudinal data are needed to confirm these findings.