White Blood Cell to HDL-C Ratio and Sarcopenia: A Dual-Cohort Analysis Including Exploratory Insights on Hepatitis B History.

BACKGROUND: Sarcopenia, driven by inflammation and lipid dysregulation, lacks inexpensive screening tools. The white blood cell to HDL-C ratio (WHR) integrates these pathways, but its utility for sarcopenia screening remains unvalidated. OBJECTIVE: This study evaluated the WHR-sarcopenia association in dual cohorts, validated it using machine learning, and explored potential effect modification of hepatitis B virus (HBV) status. METHODS: We analyzed 10 131 NHANES (2011-2018) and 7872 KNHANES (2010-2011) adults. Sarcopenia was defined via DXA using FNIH/AWGS criteria. Weighted logistic regression, restricted cubic splines, and machine learning (LASSO, XGBoost) were applied. RESULTS: Higher ln(WHR) was independently associated with sarcopenia in NHANES (adjusted OR = 2.50; 95% CI: 2.01-3.10) and consistently validated in KNHANES (OR = 1.85; 95% CI: 1.49-2.29). WHR ranked among the top predictive features across machine learning models. Exploratory stratified analysis suggests that the association between ln(WHR) and sarcopenia appears to be stronger in the HBV-exposed subgroup. However, although the formal interaction test was not significant (p = 0.270), these findings are hypothesis-generating results. CONCLUSION: WHR, a cost-free routine metric, is robustly linked to sarcopenia. Integrating it into geriatric assessments could facilitate early high-risk identification for timely interventions, while exploratory findings suggesting a possible modifying role of HBV history require prospective validation.