Ability of the Chester Step Test to detect functional impairment and mortality risk in people with interstitial lung disease

Abstract

People with interstitial lung disease (ILD) often experience disabling symptoms, which impairs their functional capacity, further accelerating disease progression. The 6-minute walk test (6MWT) has been the most widely used field test to assess functional capacity and to discriminate the mortality risk in people with ILD. Nevertheless, its application across settings (e.g., patients’ homes) is often limited due to the need of a 30 m corridor. Alternatives to assess functional capacity in these settings have been emerging, such as the 1-minute sit-to-stand test (1-minSTS) and the Chester step test (CST). However, the first does not allow exercise prescription. The CST is a simple and low-cost field test, which enables exercise prescription and requires minimal physical space to assess functional capacity. Its suitability to be used as a first-line screening tool to detect functional capacity impairment and mortality risk in people with ILD is however unknown. Thus, the aim of this study was to determine the discriminative ability of the CST in distinguishing people with ILD with or without functional impairment and low or higher risk of mortality. A retrospective cross-sectional study was conducted with stable (i.e., no history of acute cardiac events, acute exacerbations or other respiratory complications in the previous month) people with ILD. The following measures were collected: CST, 6MWT and 1-minSTS. A receiver operating characteristics (ROC) curve analysis was performed and area under the curve (AUC), sensitivity, specificity and accuracy were calculated. We determined a threshold for the CST to identify: i) functional impairment, based on published cut-offs of the percentage predicted of the 1-minSTS and the 6MWT (both 70% predicted); and, ii) mortality, based on different established cut-offs of the 6MWT (250, 330 and 350 m). The optimal cut-off points were identified by the highest Youden index. Eighty-three people with ILD (65 ± 14 years old; 45 [54.2%] female; FVC 77.7 ± 17.9%predicted; DLCO 50.3 ± 20.7% predicted) were included in the analysis. The cut-off points of the 1-minSTS (AUC = 0.73; 95%CI 0.63-0.84; 81% sensitivity; 65% specificity; accuracy = 0.72) and 6MWT (AUC = 0.91; 95%CI 0.82-0.99; 88% sensitivity; 83% specificity; accuracy = 0.86) identified a cut-off of 40.5 steps in CST to detect functional impairment in people with ILD. All cut-offs of the 6MWT identified a cut-off of 36 steps on the CST (6MWT < 250m: AUC = 0.89; 95% CI 0.80-0.97; 86% sensitivity; 80% specificity; accuracy = 0.80; 6MWT < 330m: AUC = 0.97; 95%CI 0.93-1; 96% sensitivity; 81% specificity; accuracy = 0.90; 6MWT < 350m: AUC = 0.93; 95%CI 0.86-1; 98% sensitivity; 70% specificity; accuracy = 0.90) to detect increased risk of mortality. Healthcare professionals may now use cut-offs of 40.5 and 36 steps in the CST to accurately detect people with ILD with functional impairment and/or at increased risk of mortality, respectively, which may contribute to the implementation of tailored and preventive interventions to improve functional capacity and reduce the risk of mortality in this population.