Prognostic value of the five-repetition sit-to-stand test for mortality in people with chronic obstructive pulmonary disease

Abstract

Background: Prognostic studies suggest that some musculoskeletal and functional capacity tests are independently associated with mortality in chronic obstructive pulmonary disease (COPD), but comparing their prognostic value is difficult because of differences in the selected covariates for regression modelling in those studies.

Objectives: To assess the prognostic value of five musculoskeletal and functional capacity tests in predicting mortality risk in patients with COPD after adjusting for existing and confounding prognostic factors and to compare their ability to correctly discriminate the mortality of individual participants using the 6-min walk test (6MWT). We hypothesized that the examined tests have different prognostic value.

Methods: Prospective and longitudinal study. A total of 137 patients with stable COPD (mean [SD] age 67 [8.33] years; 87% male) were recruited from a hospital in Spain during 2014 and followed for 5 years (2014-2019). No one refused and only one was lost to follow-up. The outcome measure was 5 year all-cause mortality.

Results: A total of 37 patients died within 5 years. All musculoskeletal tests were associated with 5 year all-cause mortality in Cox proportional-hazards regression models. However, only the five-repetition sit-to-stand test (5-STS) score was an independent prognostic factor (hazard ratio 1.04 per sec, 95% confidence interval 1.01-1.08) after adjusting for history of heart disease, number of previous severe exacerbations, and dyspnoea. This model explained 50.7% of the variance in mortality. This test exhibited similar discriminative ability as the 6MWT for 5 year mortality (area under the receiver operating characteristic curve: 0.741vs 0.722; p = 0.92), and a highly prognostic cut-off for discriminating (15.98 s). This cut-off had higher likelihood ratios (LRs) than the 6MWT cut-off (∼350 m), especially for negative LRs (1/LR-: 7.69vs 2.00).

Conclusions: The 5-STS is an objective measure for predicting mortality in patients with COPD and has good discriminative ability, with a cut-off for discriminating survival slight better than the 6MWT. The prognostic value of the other tests remains to be confirmed.

Keywords: 5-STS; 6MWT; Chronic obstructive pulmonary disease; Mortality; Predictors.