FibroScan

FibroScan. It is a non-invasive medical device that uses a technology called transient elastography to measure liver stiffness, which correlates with the degree of liver fibrosis. The device also incorporates a controlled attenuation parameter (CAP) to assess hepatic steatosis, or fat accumulation in the liver. Developed by the French company Echosens, it provides a rapid, painless alternative to the traditional liver biopsy for monitoring chronic liver diseases such as hepatitis C, hepatitis B, and non-alcoholic fatty liver disease (NAFLD).

Medical use

FibroScan is primarily used in hepatology clinics and by gastroenterologists to stage liver fibrosis and grade steatosis in patients with chronic liver conditions. Its applications are central to the management of viral hepatitis, alcoholic liver disease, and non-alcoholic steatohepatitis (NASH), aiding in treatment decisions and monitoring disease progression. It is also employed in large-scale screening programs, such as those conducted by the World Health Organization in regions with high prevalence of schistosomiasis or hepatitis B. The test is endorsed by professional societies like the American Association for the Study of Liver Diseases and the European Association for the Study of the Liver in specific clinical guidelines.

Technique

The procedure is performed with the patient lying supine, with the right arm fully abducted to expose the right hypochondrium. A probe containing both an ultrasound transducer and a vibrator is placed on the skin between the ribs over the right lobe of the liver. The device emits a low-frequency elastic shear wave, and the ultrasound transducer measures its propagation velocity; stiffer liver tissue conducts the wave faster. The controlled attenuation parameter (CAP) is measured simultaneously using signals from the same ultrasound pulses to quantify hepatic steatosis. The entire examination is typically completed within five to ten minutes, and results are displayed immediately on the device's screen, which is often connected to systems from companies like Epic Systems for electronic health record integration.

Interpretation

Results are expressed in kilopascals (kPa) for stiffness, with higher values indicating more advanced fibrosis; common cut-offs stratify results into stages like those of the METAVIR score (F0-F4). For example, a value below 7.0 kPa often suggests no significant fibrosis, while a value above 12.5 kPa may indicate cirrhosis. The CAP result, measured in decibels per meter (dB/m), correlates with the percentage of hepatic steatosis, often graded as S0-S3. Interpretation must consider factors like acute hepatitis, cholestasis, or congestive heart failure, which can transiently increase stiffness. Guidelines from the European Association for the Study of the Liver provide detailed frameworks for integrating these measurements into clinical decision-making.

Comparison to liver biopsy

While liver biopsy has long been the reference standard, providing a direct histological assessment from the Knodell score to the Ishak score, it is an invasive procedure with risks of bleeding, pain, and sampling error. FibroScan offers a significant advantage by assessing a liver volume approximately 100 times larger than a typical biopsy sample, reducing sampling variability. Studies published in journals like The Lancet and Gastroenterology have shown good correlation between elastography measurements and histological stages from liver biopsy across various etiologies, including autoimmune hepatitis and primary biliary cholangitis. However, it does not provide information on inflammation or specific histological features like those detailed in the NAS score for NASH.

Limitations

The accuracy of FibroScan can be reduced in patients with a high body mass index (BMI), narrow intercostal spaces, or significant ascites, as these conditions can attenuate the shear wave. It is less reliable for diagnosing early stages of fibrosis (F0-F1) compared to advanced stages, and results can be confounded by conditions causing liver congestion, such as right heart failure or Budd-Chiari syndrome. Furthermore, it cannot differentiate between the causes of fibrosis or detect other pathologies like hepatocellular carcinoma. Ongoing research, including trials registered with ClinicalTrials.gov, continues to refine its use and develop newer technologies like magnetic resonance elastography to address these limitations.

Category:Medical tests Category:Hepatology