A comparative study between ultrasound-guided-attenuation-parameter (UGAP), controlled attenuation parameter (CAP), and proton density fat fraction (PDFF) for assessment of hepatic steatosis

Gastroenterology clinics often assess hepatic steatosis using CAP-FibroScan, while radiology departments increasingly apply UGAP instead of subjective B-mode ultrasound. This study compares CAP and UGAP feasibility and diagnostic performance across steatosis stages, using PDFF as reference. Healthy controls and a cohort with known steatosis and fibrosis were examined between September 2022 and October 2024. Presence of steatosis (≥S1) defined as ≥5% PDFF, and presence of fibrosis was evaluated with MRE. Participants with even sex distribution were examined in supine and 30° left decubitus position; for UGAP, with normal (4 N) and (30 N) probe force. Diagnostic performance was evaluated by the area under the receiver operating characteristic curve (AUROC). In the group of N = 97 CAP demonstrated 91% feasibility in supine and 80% in lateral position. UGAP showed 100% feasibility for all examination techniques. The whole group was divided according to steatosis stages of PDFF. When differentiating ≥ S1, CAP supine accuracy was AUC 0.81 (95%CI: 0.71–0.92), and UGAP supine/30N accuracy was 0.88 (95%CI: 0.88–0.95). Differentiating S0 and S1 vs. S2 and S3, the CAP AUC was 0.81 (95% CI: 0.72–0.90), and the UGAP supine/30 N AUC was 0.93 (95%CI: 0.88–0.99). When differentiating S0, S1, and S2 vs. S3, the CAP AUC was 0.90 (95%CI: 0.83–0.97), and the UGAP supine/4N AUC was 0.97 (95%CI: 0.94–1.00). UGAP increased performance in both sexes using increased probe force. UGAP provides absolute feasibility and higher diagnostic performance. CAP should not be performed in left position.