Objective: Quantification of liver steatosis is clinically relevant in various liver diseases but cannot be done by conventional sonography, which only provides a qualitative assessment with significant observer variability. The aim of this study was to assess sonography as an objective tool for the quantification of liver steatosis.

Materials and methods: Files of 111 patients with chronic liver disease who were referred for sonographically guided liver biopsy were collected. A hepatorenal sonographic index was calculated on the basis of the ratio between the echogenicity of the liver and that of the right kidney cortex using histogram echo intensity. Liver steatosis was graded by histology.

Results: A significant correlation was found between histologic steatosis and the hepatorenal sonographic index (r = 0.82, p < 0.001). The validity of the hepatorenal sonographic index for the diagnosis of fatty liver was compared with liver biopsies with a steatosis level > 5%. The area under the receiver operating characteristic curve was 99.2% (95% CI, 98-100%). The optimal hepatorenal sonographic index cutoff point for the prediction of steatosis > 5% was 1.49, with sensitivity of 100% and specificity of 91%. The optimal hepatorenal sonographic index cutoff point for the prediction of steatosis >/= 25% was 1.86, with sensitivity of 90% and specificity of 90%. The optimal hepatorenal sonographic index cutoff point for the prediction of steatosis >/= 60% was 2.23, with sensitivity of 90% and specificity of 93%.

Conclusion: The hepatorenal sonographic index is a sensitive noninvasive method for steatosis quantification. It can diagnose small amounts of liver fat that would be missed by conventional sonography. It is reproducible and operator independent and can serve as an efficient tool to follow patients with steatosis and evaluate the efficacy of new treatment techniques.