Cutoff Points for Step Count to Predict 1-year All-Cause Mortality in Patients with Idiopathic Pulmonary Fibrosis

Background: Although physical activity is associated with mortality in patients with idiopathic pulmonary fibrosis (IPF), reference values to interpret levels of physical activity are lacking. Objectives: This study aimed to investigate the prognostic significance of physical activity assessed by step count and its cutoff points for all-cause mortality. Methods: We measured physical activity (steps per day) using an accelerometer in patients with IPF at the time of diagnosis. Relationships among physical activity and mortality, as well as cutoff points of daily step count to predict all-cause mortality were examined. Results: Eighty-seven patients (73 males) were enrolled. Forty-four patients (50.1%) died during the follow-up (median 54 months). In analysis adjusting for Gender-Age-Physiology stage and 6-min walk distance, daily step count was an independent predictor of all-cause mortality (hazard ratio (HR) = 0.820, 95% confidence interval (CI) = 0.694-0.968, p = 0.019). The optimal cutoff point (receiving operating characteristic analysis) for 1-year mortality was 3,473 steps per day (sensitivity = 0.818 and specificity = 0.724). Mortality was significantly lower in patients with a daily step count exceeding 3,473 steps than in those whose count was 3,473 or less (HR = 0.395, 95% CI = 0.218-0.715, p = 0.002). Conclusions: Step count, an easily interpretable measurement, was a significant predictor of all-cause mortality in patients with IPF. At the time of diagnosis, a count that exceeded the cutoff point of 3,473 steps/day more than halved mortality. These findings highlight the importance of assessing physical activity in this patient population.