The neutrophil-percentage-to-albumin ratio (NPAR) shows a nonlinear correlation with all-cause mortality in patients with anemia.

The neutrophil percentage-to-albumin ratio (NPAR) is an emerging indicator of inflammation that has been associated with the prognosis of various diseases, including hypertension, diabetes, and cardiovascular disease. NPAR is calculated by multiplying the neutrophil percentage by 100 and dividing it by the albumin value. This study aimed to evaluate the predictive value of NPAR for all-cause mortality in anemic patients. We employed Kaplan-Meier analysis, multiple regression models, restricted cubic splines (RCS), and threshold effect analysis to explore these associations. This study included 3,258 anemic individuals. The relationship between NPAR and all-cause mortality was evaluated using Kaplan-Meier analysis and multiple regression models. RCS curves were employed to assess potential nonlinear relationships, while threshold effect analysis was used to identify breakpoints in the association between NPAR and mortality risk. Subgroup analyses were conducted to examine variations in this relationship across different population strata. The study population included 3,258 anemic patients, with a mean follow-up period of 94.3 months. During follow-up, 904 participants (27.75%) died. Kaplan-Meier analysis revealed that individuals in the highest NPAR quartile (Q4) exhibited significantly higher cumulative mortality compared with those in the lowest quartile (Q1) (p < 0.001). Multiple regression analysis showed that, in model 3, each unit increase in NPAR among individuals in the highest quartile was associated with a 51.8% increased risk of all-cause mortality. RCS and threshold effect analyses revealed a nonlinear relationship between NPAR and mortality, with a breakpoint at NPAR = 15.119. Below this threshold, no statistical association was observed, while above the threshold, NPAR was positively associated with increased mortality risk. Subgroup analysis revealed a significant positive correlation between anemia in individuals under 60 years of age, with diabetes mellitus and a body mass index ≥ 30 kg/m², and all-cause mortality. Our findings indicate that elevated NPAR is independently associated with increased all-cause mortality in anemic individuals. The nonlinear relationship and identified breakpoint suggest that NPAR may serve as a valuable prognostic biomarker for mortality risk in this population. Further research should focus on the clinical utility of NPAR in guiding therapeutic interventions for anemia.