Controlled attenuation parameter and alcoholic hepatic steatosis: Diagnostic accuracy and role of alcohol detoxification

Authors
Maja Thiele, Vanessa Rausch, Gabriele Fluhr, Maria Kjærgaard, Felix Piecha, Johannes Mueller, Beate Katharina Straub, Monica Lupșor-Platon, Victor De-Ledinghen, Helmut Karl Seitz, Sönke Detlefsen, Bjørn Madsen, Aleksander Krag and Sebastian Mueller

Background & Aims
Controlled attenuation parameter (CAP) is a novel non-invasive measure of hepatic steatosis, but it has not been evaluated in alcoholic liver disease. Therefore, we aimed to validate CAP for the assessment of biopsy-verified alcoholic steatosis and to study the effect of alcohol detoxification on CAP. 

Methods
This was a cross-sectional biopsy-controlled diagnostic study in four European liver centres. Consecutive alcohol-overusing patients underwent concomitant CAP, regular ultrasound, and liver biopsy. In addition, we measured CAP before and after admission for detoxification in a separate single-centre cohort. 

Results
A total of 562 patients were included in the study: 269 patients in the diagnostic cohort with steatosis scores S0, S1, S2, and S3 = 77 (28%), 94 (35%), 64 (24%), and 34 (13%), respectively. CAP diagnosed any steatosis and moderate steatosis with fair accuracy (area under the receiver operating characteristic curve [AUC] ≥S1 = 0.77; 0.71–0.83 and AUC ≥S2 = 0.78; 0.72–0.83), and severe steatosis with good accuracy (AUC S3 = 0.82; 0.75–0.88). CAP was superior to bright liver echo pattern by regular ultrasound. CAP above 290 dB/m ruled in any steatosis with 88% specificity and 92% positive predictive value, while CAP below 220 dB/m ruled out steatosis with 90% sensitivity, but 62% negative predictive value. In the 293 patients who were admitted 6.3 days (interquartile range 4–6) for detoxification, CAP decreased by 32 ± 47 dB/m (  p  <0.001). Body mass index predicted higher CAP in both cohorts, irrespective of drinking pattern. Obese patients with body mass index ≥30 kg/m  2  had a significantly higher CAP, which did not decrease significantly during detoxification. 

Conclusions
CAP has a good diagnostic accuracy for diagnosing severe alcoholic liver steatosis and can be used to rule in any steatosis. In non-obese but not in obese, patients, CAP rapidly declines after alcohol withdrawal. 

Lay summary
CAP is a new ultrasound-based technique for measuring fat content in the liver, but has never been tested for fatty liver caused by alcohol. Herein, we examined 562 patients in a multicentre setting. We show that CAP highly correlates with liver fat, and patients with a CAP value above 290 dB/m were highly likely to have more than 5% fat in their livers, determined by liver biopsy. CAP was also better than regular ultrasound for determining the severity of alcoholic fatty-liver disease. Finally, we show that three in four (non-obese) patients rapidly decrease in CAP after short-term alcohol withdrawal. In contrast, obese alcohol-overusing patients were more likely to have higher CAP values than lean patients, irrespective of drinking. 

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