Association between the alkaline phosphatase-to-albumin ratio and recorded early all-cause mortality within 90 days of admission in patients with heart failure: a retrospective cohort study in a Chinese population

Background APAR combines alkaline phosphatase and albumin, two routine laboratory measurements. We examined its association with recorded early all-cause mortality within 90 days of admission in hospitalized patients with heart failure (HF), prioritizing continuous APAR over a mortality-derived cutoff. Methods We analyzed version 1.3 of the Zigong Heart Failure Database. Among 2,008 patients, 1,906 had calculable APAR and a recorded vital-status outcome within 90 days; 37 deaths were recorded. Exact event times were available for 1,905 patients (36 deaths). The primary model assessed standardized ln(APAR), adjusting for the eight released age categories as a 1–8 ordinal score, sex, log(BNP), eGFR, sodium, and CCI, with NYHA class stratification. Mortality timing, post-discharge survival, hemoglobin adjustment, and E-values were examined in sensitivity analyses. Results Recorded all-cause mortality within 90 days of admission was 1.94%. In the complete-case model ( n = 1,824; 36 deaths), each 1-SD increase in ln(APAR) was associated with higher mortality (HR 1.375, 95% CI 1.024–1.846; P = 0.034), whereas raw APAR per 1 U/g was not (HR 1.146, 95% CI 0.988–1.330; P = 0.072). The spline showed an overall association ( P = 0.025) and nonlinearity ( P = 0.023). Nine of 37 deaths were confirmed in-hospital. Among 1,897 patients discharged without recorded in-hospital death, 28 died within 90 days: 15 on a later calendar date, 12 on the discharge date, and one with missing exact timing. In the strict post-discharge analysis, the adjusted HR was 1.460 (95% CI 0.931–2.289; P = 0.099; 15 events). APAR showed modest discrimination (AUC 0.698), while incremental value was limited: Δ C-index 0.018 ( P = 0.104), IDI 0.0019 (95% CI −0.0035 to 0.0252), small decision-curve gains, and continuous NRI 0.179 (95% CI −0.129 to 0.577). Conclusion Higher admission ln(APAR) was associated with recorded early all-cause mortality within 90 days of admission, but the association was modest, nonlinear, scale-dependent, and based on few events. Post-discharge estimates were directionally consistent but imprecise. External validation is required before APAR or any cutoff is used for clinical risk stratification.