Noninvasive quantitative estimation of hepatic steatosis by ultrasound: A comparison of the hepato-renal index and ultrasound attenuation index

Aims: To compare the accuracy of the ultrasound attenuation index (USAI) and hepato-renal index (HRI) for the diagnosis of hepatic steatosis (HS). Material and methods: Two hundred and twenty-four potential living hepatic donors underwent US and subsequent US-guided liver biopsy. The USAI was calculated from US images with an 8 MHz transducer and HRI was measured on sagittal images with a clear visualization of both the liver and kidney. Using histological degrees of HS as the reference standard, we compared the performance of USAI and HRI for diagnosing HS=5% and =30% by receiver operating characteristic curve analysis. The interobserver agreement was evaluated by using intraclass correlation coefficients (ICCs) or Bland-Altman statistics. Results: Histologic degree of HS was 0-70% (median, 5%). HRI showed a tendency towards higher accuracy than USAI for diagnosing HS≥5% (the area under the ROC curve, 0.856 vs. 0.820; p=0.279) and ≥30% (0.937 vs. 0.909; p=0.378) without statistical significance. There was an excellent interobserver agreement for both USAI and HRI (ICC=0.931 and 0.973, respectively). According to the Bland-Altman method, the 95% limits of difference between two readers for HS were -8.5% to 6.6% by USAI and -4.8% to 6.2% by HRI. Most patients would have the difference of calculated HS by USAI (74.0%) and HRI (96.0%) from different operators within a range of ±5%. Conclusions: Although statistically insignificant, HRI was superior to USAI for the diagnosis and quantitative estimation of HS in terms of diagnostic performance, including accuracy and reproducibility.