Immature Platelet Fraction and Long-Term Mortality in Acute Coronary Syndrome Across the Body Mass Index Spectrum

Background and Aim The immature platelet fraction (IPF) reflects platelet turnover. We examined the association of admission IPF with long-term all-cause mortality in acute coronary syndrome (ACS), and whether IPF varies with body mass index (BMI). Methods and Results In a prospective single-center registry of consecutive patients with ACS (July 2019-August 2026), 3,405 had BMI and admission IPF (Sysmex XN-2000) available. Over a median follow-up of 3.0 years, 506 of 3,403 patients with follow-up (14.9%) died. Five-year mortality was 15.1%, 17.5% and 23.0% in the low (<2.7%), intermediate and high (≥6.0%) IPF groups (log-rank p=0.002). After adjustment for 17 clinical covariates, high IPF (HR 1.29, 95% CI 1.06-1.58) and continuous IPF (HR 1.04 per 1%, 95% CI 1.02-1.07) were associated with mortality, without effect modification by BMI (p-interaction = 0.077). Adding IPF only marginally improved discrimination (C-statistic 0.840 to 0.841). IPF was not correlated with BMI (Spearman ρ = 0.007, p=0.67), and after adjustment class III obesity was not associated with higher IPF than normal weight (geometric mean ratio 1.04, 95% CI 0.88-1.22). BMI had a U-shaped association with long-term mortality (non-linearity p < 0.001). Conclusions In ACS, higher admission IPF was independently associated with long-term all-cause mortality across the BMI spectrum, with limited incremental prognostic value, whereas IPF did not differ across BMI categories. External validation is required.