To explore the predictive value of hemoglobin-to-age ratio (HAR) for 28-day mortality in patients with community-acquired pneumonia (CAP).

Based on the medical information mart for intensive care Ⅳ (MIMIC-Ⅳ) database of American critical care medicine, 6 203 patients who were admitted to the ICU for the first time and met the diagnostic criteria for CAP were included. Demographic information, comorbidities, vital signs, disease severity score, laboratory indicators, and therapeutic measures were extracted. Patients were divided into a Q1 group (0.650 ≤ HAR < 1.200, n = 1 551), a Q2 group (1.200 ≤ HAR < 1.460, n = 1 551), a Q3 group (1.460 ≤ HAR < 1.830, n = 1 552), and a Q4 group (1.830 ≤ HAR ≤ 7.520, n = 1 549) according to HAR values. Kaplan-Meier survival analysis, multivariate Cox regression, and restricted cubic spline (RCS) models were used to explore the association between HAR and 28-day all-cause mortality in CAP patients. The predictive value of HAR for death within 28 days was also clarified by constructing a multivariate Cox model.

There were statistically significant differences in age, body weight, gender, tumor, kidney disease, heart rate, pulse oxygen saturation, acute physiology score Ⅲ, Oxford acute severity of illness score, hemoglobin, 24-hour output, invasive mechanical ventilation use, ICU stay days, and 28-day mortality among patients in the Q1-Q4 groups (all P < 0.05). Based on 28-day survival status, 6 203 patients were divided into a survival group (4 435 patients) and a mortality group (1 768 patients). The age, body mass, HAR, complication, vital signs, disease severity score, laboratory examination, 24-hour output, invasive mechanical ventilation use, vasopressor use, length of hospital stay, and ICU admission duration were compared between the two groups, and there were significant differences (all P < 0.05). The Kaplan-Meier survival curve revealed a statistically significant difference in survival rates among the Q1-Q4 groups (χ² = 118.208, P < 0.001), with the Q4 group showing a markedly higher survival rate than the Q1-Q3 group (χ² = 92.768, P < 0.001). Cox regression showed that HAR was an independent influencing factor for the 28-day mortality of CAP patients [hazard ratio (HR) = 0.651, 95% confidence interval (CI) (0.586, 0.722), P < 0.001]. The HR and 95%CI for 28-day mortality decreased with the increase of HAR quartiles, ranging from 1.000 to 0.883 [95%CI (0.780, 0.999)], 0.783 [95%CI (0.687, 0.893)], and 0.534 [95%CI (0.456, 0.625)] respectively. Further analysis using RCS showed that HAR had a non-linear relationship with the 28-day mortality of patients admitted to the ICU. When HAR was below 2.872, the mortality increased sharply with the decrease of HAR (P < 0.001).

HAR is negatively correlated with 28-day mortality in CAP patients. HAR levels can help identify patients at a higher risk of adverse outcomes, guiding clinicians in stratification and early intervention.