Steatosis assessment by controlled attenuation parameter (CAP™)

Abstract

Steatosis is a reversible and benign condition. However, recent studies have shown that it can be independently associated with fibrosis progression, a lower response rate to antiviral treatment, or even the occurrence of hepatocellular carcinoma, especially in the context of metabolic syndrome. With the increasing prevalence of non-alcoholic fatty liver disease, the evaluation of steatosis is essential for routine patient care but also in clinical studies. A non-invasive parameter, controlled attenuation parameter (CAP), based on vibration-controlled transient elastography (VCTE), has been developed to assess liver steatosis on the FibroScan device, concomitantly to liver stiffness measurement. CAP provides a rapid and inexpensive bedside assessment of liver steatosis. Based on multiple studies for various liver diseases, CAP cutoff values for S1, S2, and S3 are 240, 260, and 290 dB/m with AUROCs from 0.70 to 0.94, respectively. Usage of the XL-CAP requires ca. 20% higher cutoff values if compared to the M-CAP probe. It is recommended to fast 2 h prior to CAP measurements since food intake can steatosis-independent CAP modulation. The purpose of this chapter is to explain the CAP measurement principle and rationale and to give an exhaustive review of its diagnostic performance in various chronic liver diseases. Results relative to its ability to follow up disease progression or response to treatment will also be provided. Eventually, results about CAP reproducibility and factors that may influence CAP will be discussed.