Prognostic value of distance–saturation product in COPD: Korean nationwide cohort study

Background The Distance-Saturation Product (DSP), calculated by multiplying six-minute walk distance (6MWD) by lowest oxygen saturation, is a composite physiologic marker of exercise capacity and gas exchange impairment. Although DSP has shown prognostic potential in Western COPD cohorts, its utility and optimal threshold in Asian populations remain unestablished. This study evaluated whether DSP <290 m% predicts exacerbations and mortality in COPD, compared with the BODE index. Methods We analyzed 1995 patients with valid 6MWD data from the Korean COPD Subgroup Study, a nationwide prospective cohort. DSP was dichotomized at 290 m% based on restricted cubic spline analyses. Primary outcomes were 3-year acute exacerbations (AEs) and all-cause mortality. Associations were evaluated using multivariable logistic, negative binomial, and Cox regression models, with the BODE index as comparator. Results Patients with DSP <290 m% had more severe symptom, worse airflow limitation, more frequent prior-year AEs. Low DSP was independently associated with more frequent severe (aIRRs 2.27–2.54) and moderate (aIRRs 1.42–1.52) exacerbations, with significantly increased moderate AE risk observed only in year 1 (aOR 1.60; 95% CI: 1.05–2.45). Patients with low DSP also had higher 3-year mortality (9.2% versus 2.6%, p<0.001), with a significantly increased risk of death (aHR 2.74; 95% CI: 1.68–4.45). DSP-based models demonstrated superior discrimination for 3-year mortality (AUC 0.673) compared to the BODE index (AUC 0.636). Conclusions DSP is a simple, scalable prognostic marker in COPD patients. A threshold of 290 m% identifies patients at higher risk of exacerbations and mortality.