Nonlinear relationship between hemoglobin-to-age ratio and 28-day mortality in patients with chronic obstructive pulmonary disease: A retrospective cohort study from MIMIC-IV database

Chronic obstructive pulmonary disease (COPD) outcomes are closely linked to both age and hemoglobin levels, with the hemoglobin-to-age ratio (HAR) emerging as a significant factor that integrates these 2 elements. However, the specific influence of HAR on COPD prognosis remains to be fully understood. This study investigated the prognostic significance of the HAR in patients with COPD. We retrieved information from the Medical Information Mart for Intensive Care-IV (version 3.1) database in the retrospective cohort study. Participants included were those diagnosed with COPD admitted to the intensive care unit. For all participants, clinical measurements, lab data, and existing medical conditions were collected to examine the link between HAR and mortality within 28 days. Multivariable Cox regression analysis, Kaplan–Meier survivor analysis, restricted cubic spline and stratified interaction analysis were applied to determine the independent link between HAR and mortality within 28 days. A total of 5811 individuals with COPD were included in the study. The mean age of the participants was 72.0 years, with a standard deviation of 11.0 years; 54.2% of the cohort were male. The 28-day mortality rate across the cohort was 18.8%. The analysis demonstrated a nonlinear relationship between the HAR and the risk of 28-day mortality. Distinct slopes were identified, showing that the relationship between HAR and mortality varied significantly above and below the inflection point, located at approximately 0.19. On the left side of the inflection point the effect size was 0.001 (hazard ratio [HR] = 0.001, 95% confidence interval: 0–0.021, P < .001), and on the right side of the inflection point (HR = 7.693, 95% confidence interval: 0.018–3271.597, P = .5065). A nonlinear association was identified between HAR and mortality within 28 days among critically ill patients with COPD. HAR is associated with 28-day mortality and may serve as a candidate marker for further validation.