Predictive role of red blood cell distribution width and hemoglobin-to-red blood cell distribution width ratio for mortality in patients with COPD: evidence from NHANES 1999–2018

Higher red blood cell distribution width (RDW) levels are associated with mortality in patients with chronic obstructive pulmonary disease (COPD). However, more convincing evidence is still lacking, and the relationship between hemoglobin-to-red blood cell distribution width ratio (HRR) and mortality in patients with COPD remains unclear. This study is a prospective cohort study that includes 3,745 adult patients with COPD from the National Health and Nutrition Examination Survey (NHANES) database spanning from 1999 to 2018 in the United States. COX proportional hazards regression analysis, Kaplan–Meier survival curves and restricted cubic spline models were employed to investigate the association of RDW and HRR levels with mortality. Time-dependent receiver operating characteristic curve (ROC) analysis was conducted to evaluate the accuracy of RDW and HRR in predicting mortality in patients with COPD. Higher RDW level was positively associated with increased risk of all-cause mortality (HR = 1.16, 95% CI = 1.11–1.21, P < 0.001), cardiovascular disease (CVD) mortality (HR = 1.13, 95% CI = 1.06–1.21, P < 0.001), and chronic lower respiratory disease (CLRD) related mortality (HR = 1.15, 95% CI = 1.05–1.25, P = 0.003) after adjusting for various potential confounders. HRR was inversely associated with all-cause mortality (HR = 0.14, 95% CI = 0.08–0.25, P < 0.001), CVD mortality (HR = 0.12, 95% CI = 0.05–0.31, P < 0.001). HRR has no significant correlation with CLRD-related mortality. The time-dependent ROC curve showed that RDW exhibited area under the curves (AUCs) of the 5- and 10-year survival rates were 0.707 and 0.714 for all-cause mortality and 0.686 and 0.698, respectively, for CVD mortality. HRR yielded AUCs of the 5- and 10-year survival rates were 0.661 and 0.653 for all-cause mortality and 0.654 and 0.66, respectively, for CVD mortality. Higher RDW levels were positively associated with an increased risk of mortality in patients with COPD. HRR levels were negatively correlated with the risk of all-cause and CVD mortality. The predictive value of HRR for mortality in these patients is lower than that of RDW.