Correlation between the red blood cell distribution width to albumin ratio and mortality rate in patients with bronchial asthma

The red blood cell distribution width-to-albumin ratio (RAR) has emerged as an important biomarker for evaluating the prognosis of several respiratory diseases. However, there is currently limited research on the correlation between RAR and mortality in patients with bronchial asthma. This study employed a multicentre cohort design: (1) The National Health and Nutrition Examination Survey (NHANES) cohort: comprising 5,365 adult asthma patients, the study analysed the independent association between RAR and mortality using methods such as the Cox proportional hazards model and restricted cubic splines (RCS); (2) The MIMIC-IV cohort: comprising 1,474 ICU patients with asthma, this cohort assessed the independent predictive value of RAR for 30-day all-cause mortality, evaluated its incremental value, and utilised a group-based trajectory model (GBTM) to identify the longitudinal trajectory of RAR over time and its association with prognosis; (3) eICU-CRD cohort: comprising 859 ICU patients with asthma, to validate the consistency of the aforementioned associations in a multicentre setting; (4) NWICU cohort: comprising 177 ICU patients with asthma, to assess robustness across databases and time periods specific to the database. In NHANES, each one‑unit increase in RAR was associated with a 71% higher risk of all‑cause mortality (HR = 1.71, 95% CI: 1.46–2.00). RCS showed a non‑linear positive association (inflection point: 3.13); Q4 vs. Q1 conferred a 125% higher risk (HR = 2.25). In MIMIC‑IV, RAR independently predicted 30‑day mortality (HR = 1.23); adding RAR to SAPS II improved AUC from 0.787 to 0.810 (ΔAUC = 0.023, P < 0.001). Trajectory analysis identified three patterns; patients with persistently high RAR had a 2.25‑fold higher death risk (HR = 2.25). Each unit increase in RAR was associated with a 21% higher mortality risk (HR = 1.21, 95% CI: 1.14–1.29, P < 0.001) in eICU‑CRD and a 42% higher mortality risk (HR = 1.42, 95% CI: 1.11–1.81, P = 0.005) in NWICU. RAR is non-linearly positively associated with mortality in patients with bronchial asthma and has both static and dynamic prognostic value; however, this requires further validation through prospective studies.