Cut-off points of the 1-minute sit-to-stand test to detect functional impairment and mortality risk in people with COPD

Abstract

Introduction: Functional status is a key outcome in people with chronic obstructive pulmonary disease (COPD) and can be defined as an individual’s ability to perform normal daily activities required to meet basic needs, fulfill usual roles, and maintain health and well-being. The 1-minute sit-to-stand test (1-min STS) is a wellestablished measure to assess functional status in people with COPD that can be used in different settings (e.g., office, clinic, hospital, home) with limited resources (i.e., a chair and a stopwatch). This test is a strong predictor of exacerbations, hospitalizations and mortality in people with COPD. Yet, cut-off points to determine functional impairment with the 1-min STS in people with COPD are lacking for use in clinical practice. Recently, our group established a cut-off (19.5 repetitions) for increased mortality risk, however, it still lacks external validation. Objectives: To explore the predictive ability of the 1-min STS to detect functional impairment and the validity of the previously established cut-off for increased risk of mortality in people with COPD. Methods: A cross-sectional study was conducted with people with COPD. Age, sex, body mass index (BMI), lung function, the 1-min STS and the five-repetitions sit-to-stand tests were collected. We used two cut-offs for the five-repetitions sit-to-stand test known to be associated with low functional performance (12.1 seconds) and increased risk of mortality (15.98 seconds) in people with COPD. Receiver operating characteristics analysis (ROC) was performed and the area under the curve (AUC), sensitivity, specificity, and accuracy were calculated. The optimal cut-off points were identified by the highest Younden index. Results: In total, 302 people with COPD (67.5 ± 10.4 years; 79.1% male; BMI 26.7 ± 4.6 kg/m²; FEV1 55.2 ± 20.4%predicted) participated. Cut-off points in the 1-min STS of 23.5 repetitions for low functional performance (AUC = 0.92; 95%CI 0.89-0.95; 96.4% sensitivity; 80.9% specificity; accuracy = 0.84) and 18.5 repetitions for increased risk of mortality (AUC = 0.97; 95%CI 0.94-0.987; 95.5% sensitivity; 88.6% specificity; accuracy = 0.89) were found in people with COPD. Conclusions: The 1-min STS showed an outstanding discriminative ability and excellent accuracy in determining low functional performance and increased risk of mortality in people with COPD. A cut-off of 23.5 repetitions can be used to identify people with functional impairment. The cut-off point found for increased risk of mortality is similar to the previously published using the 6-minute walk test as an anchor, reinforcing the validity of this cut-off. These cut-offs support healthcare professionals in tailoring an appropriate management plan for this treatable trait and might possibly contribute to the implementation of timely preventive or palliative strategies.