Conicity index and lipid-metabolic indices for ultrasound-diagnosed hepatic steatosis in HBsAg-positive adults: a cross-sectional study emphasizing normal BMI

Hepatic steatosis commonly coexists with HBsAg positivity, but how low-cost anthropometric and lipid-metabolic indices compare in adjusted cross-sectional association and discrimination, particularly among adults with normal BMI, remains uncertain. We analyzed 7984 HBsAg-positive individuals who underwent routine health examinations between March 2014 and December 2017. Discrimination and incremental model performance were evaluated in a common complete-case sample ( N = 7670; 1634 events) using areas under the receiver operating characteristic curve (AUCs) and paired DeLong tests, with pre-specified subgroup analyses by sex, age group, BMI category, and alanine aminotransferase status. Restricted cubic splines were used to assess nonlinearity for the conicity index, TyG-WC, and TyG-BMI, and 1st/99th percentile winsorization was used to assess sensitivity to extreme values. Hepatic steatosis was identified in 1681 participants (21.1%). The conicity index showed a graded adjusted cross-sectional association with steatosis (extended adjusted OR 1.84, 95% CI 1.64–2.07, per 0.1-unit increase) but lower standalone discrimination (AUC 0.749). TyG-WC and TyG-BMI showed the highest and similar discrimination (AUC 0.868 vs 0.865; DeLong P = 0.155). In the common complete-case sample, adding TyG-WC to age and sex increased the AUC from 0.640 to 0.871. Among 3783 adults with normal BMI, 217 (5.7%) had steatosis; TyG-WC retained an AUC of 0.842, while the conicity index association was stronger than in the overweight and obesity strata (OR 2.26, 95% CI 1.81–2.82, per 0.1-unit increase; P for interaction < 0.001). Spline analyses indicated nonlinearity, whereas the winsorized estimates were similar to the primary estimates. TyG-WC and TyG-BMI showed similar and the highest discrimination for concurrent ultrasound-diagnosed hepatic steatosis in HBsAg-positive adults, including those with normal BMI. The conicity index showed a stronger adjusted cross-sectional association in the normal-BMI stratum but lower standalone discrimination. Because they use routinely collected anthropometric and laboratory measurements, TyG-WC and TyG-BMI warrant prospective external evaluation as low-cost triage aids; however, the present cross-sectional findings do not establish clinical cutoffs or screening benefit.