BMI-C as a predictor of hepatic steatosis: validation in the NHANES 2017–2023 cohort with liver elastography

AbstractIntroduction: Metabolic dysfunction-associated steatotic liver disease (MASLD) affects30–40% of adults globally. BMI, the primary anthropometric screening tool, does notdistinguish fat mass from lean mass and fails to detect steatosis in individuals with normalBMI (lean NAFLD). BMI-C (Body Morphometric Index – Corrected) is a proprietary index thatcorrects the dimensional error of BMI.Objective: To validate BMI-C as a predictor of hepatic steatosis in an NHANES cohortwith liver elastography.Methods: Cross-sectional study with n=5,013 adults (≥20 years) from NHANES 2017–2018 and 2021–2023 with valid FibroScan. Primary outcome: CAP ≥ 280 dB/m (S3).Secondary outcomes: CAP ≥ 268 (S2+), CAP ≥ 248 (S1+), stiffness ≥ 8 kPa (F2+). AUC with95% CI by bootstrap (2,000 resamples). DeLong test for comparison. Mediation by insulin.Stratification by BMI.Results: S3 prevalence = 38.0%. AUC for S3: BMI-C = 0.794 [0.781–0.806]; BMI =0.781 [0.767–0.793]; waist circumference = 0.802 [0.790–0.814]. DeLong test confirmedBMI-C outperforms BMI (ΔAUC = +0.0132, p < 0.0001). In BMI < 25 (n=1,417), BMI-C AUC= 0.736 [0.692–0.775]; BMI AUC = 0.625 [0.580–0.667]; difference +0.111. Insulin mediates24.9% of the effect (95% CI: 21.8–28.1%); in BMI < 25, 13.4%; in BMI ≥ 25, 26.2%. BMI-C ×insulin interaction significant (LR = 16.50, p < 0.0001). In the highest tertile of both, S3prevalence = 75.3%; in the lowest tertile, 6.4%. Optimal cut-off (Youden) for S3 = 1.318. Conclusion: BMI-C predicts hepatic steatosis with AUC 0.794, surpassing BMI by+0.013 with statistical significance (p < 0.0001). In individuals with normal BMI, where BMI fails (AUC 0.625), BMI-C detects lean NAFLD (AUC 0.736). Insulin mediates 25% of theeffect, with synergistic interaction. BMI-C is a viable tool for primary care screening.