Neutrophil percentage-to-albumin ratio is associated with low muscle mass risk in rheumatoid arthritis: evidence from a hospital-based cohort and NHANES validation.

INTRODUCTION: Sarcopenia is an important extra-articular complication of rheumatoid arthritis (RA), caused by chronic inflammation, nutritional deficiency, and metabolic changes. Muscle mass is a key diagnostic indicator. The neutrophil percentage to albumin ratio (NPAR) is a readily available biomarker calculated from neutrophil percentage and serum albumin; however, its relationship with muscle mass reduction and prognosis in RA patients requires further clarification. METHODS: The analysis was conducted on a cohort of 659 patients with RA who were admitted to hospital between Jan 2021 and Dec 2025. Low muscle mass (LMM) was defined using the 2019 Asian Working Group for Sarcopenia (AWGS) criteria with dual energy X-ray absorptiometry. The NPAR was calculated as neutrophil percentage divided by serum albumin. We performed multivariable logistic regression, restricted cubic spline (RCS) analysis, sensitivity analysis, receiver operating characteristic analysis, and subgroup analyses, with parallel analysis using 375 RA participants from the NHANES. Cox proportional hazards models assessed the association between NPAR and all-cause mortality in RA patients with LMM. RESULTS: Among 167 hospitalized RA patients with LMM, elevated NPAR was independently associated with LMM risk after adjusting for confounders, with consistent sensitivity analyses. RCS analysis revealed a positive linear relationship. Patients with high NPAR showed significantly higher LMM prevalence than those with low NPAR. NPAR demonstrated strong discriminatory ability (AUC = 0.80, optimal cutoff = 9.55). In the NHANES cohort, elevated NPAR remained independently associated with LMM, with participants in the highest NPAR quartile substantially more likely to have LMM than those in the lowest quartile. Additionally, higher NPAR was associated with increased all-cause mortality in RA patients with LMM during follow-up. CONCLUSION: Higher NPAR is independently associated with LMM risk-a central diagnostic component of sarcopenia-in patients with RA, and may also predict worse survival among those with reduced muscle mass. These findings suggest that NPAR could facilitate early risk stratification and prognosis assessment for sarcopenia in RA clinical practice.