Controlled Attenuation Parameter

During transient elastography, a mechanical vibration produces shear waves in the liver while ultrasound tracks the weakening of signal energy as it travels through tissue. Fatty tissue causes greater attenuation, meaning more energy is lost along the path. The system converts this attenuation into a CAP value, expressed in decibels per meter, for clinical assessment of steatosis.

A higher CAP value indicates greater ultrasound energy attenuation through the liver, which is consistent with more hepatic steatosis. The result should not be interpreted in isolation as a complete diagnosis or measure of overall liver health. Clinicians consider CAP together with liver stiffness, medical history, and laboratory findings to support a broader assessment.

Inflammation, fibrosis, and body habitus can influence CAP interpretation, so the measurement may not reflect liver fat alone in every patient. These factors are important because they can affect tissue properties or measurement conditions. Clinical teams therefore place the numerical result in context rather than relying on a single CAP value to characterize disease.

CAP and liver stiffness measurement provide different types of information from transient elastography. CAP focuses on attenuation of ultrasound energy as an indicator of hepatic steatosis, whereas liver stiffness contributes separate information about the mechanical properties of liver tissue. Using both results can give clinicians a more informative picture than either measurement considered alone.

The examination uses transient elastography, in which a mechanical vibration generates shear waves and ultrasound signals follow their passage through liver tissue. The system evaluates how rapidly the ultrasound energy weakens and reports the result as a CAP value in decibels per meter. This produces information without requiring a liver biopsy, while interpretation still incorporates clinical findings.

Clinicians use CAP to support screening for fatty liver disease, evaluate patients being assessed for hepatic steatosis, and follow changes over time. It can also contribute to treatment assessment when considered with other clinical information. Because the method is noninvasive, it provides a way to obtain relevant liver-fat information without making biopsy the routine measurement approach.

CAP measures attenuation associated with hepatic steatosis, but clinical interpretation can be affected by inflammation, fibrosis, body habitus, and other conditions. Medical history and laboratory findings help clinicians judge whether the result fits the overall clinical picture. Combining these sources supports more careful screening, monitoring, and treatment assessment than interpreting the CAP value alone.