Importance of fibrosis (scarring) in fatty liver
Non-alcoholic fatty liver disease (NAFLD) or fatty liver if continues for long time can cause fibrosis (scarring or shrinkage) in the liver which ultimately may damage the liver and can cause cirrhosis liver and even liver cancer. Hence it is very important to determine the presence and extent of fibrosis in patients with fatty liver as early as possible so as to treat it and to predict the outcome in those who already have advanced fibrosis and cirrhosis.
Limitations of doing liver biopsy
Traditionally liver biopsy (taking liver piece from the liver by a needle) remains the gold standard for determination of hepatic fibrosis in NAFLD. However, liver biopsy is an invasive procedure (putting needle in the liver) and may be associated with complications like pain and bleeding. Moreover, the sample obtained with liver biopsy is very small and sometimes, may not represent the disease process going on in the whole liver. Liver biopsy sample has to be sent to pathology lab and the whole process of interpretation of the biopsy takes few days before the final report, which may also be associated with some inter- and intra-observer variation among the pathologists analysing the liver biopsy. In addition, because of the invasive nature of the liver biopsy, it is difficult to do it repeatedly in order to assess the effect of various treatment modalities in NAFLD.
Fibroscan for the assessment of liver fibrosis (scarring)
Hence there has always been a need for various non-invasive test which are simple, accurate, less time consuming and could act as an alternative to liver biopsy for the assessment of liver fibrosis in patients with fatty liver. Fibroscan or Transient Elastography is one such alternative to liver biopsy and has the advantage of being purely non-invasive, safe, accurate, operator-independent and can be repeated any number of times.
Technique of Fibroscan
Patient needs to come for the Fibroscan test with 2-3 hours of fasting and the test is done with a machine similar to ultrasound machine and the examination takes less than five minutes and the report is given immediately to the patient. The principle of Fibroscan is to measure the hepatic fibrosis by assessment of liver stiffness by assessing the speed of the travelling shear waves generated by the transducer (probe) of the machine. Higher the liver stiffness or hepatic fibrosis, higher would be the Fibroscan value which is measured in kilopascals (kPa) and varies from 2.5 to 75 kPa. In patients with overweight and obesity and with high fat below the skin of the right side of the chest (where probe is kept for examination), the values may not be accurate with the standard probe (M probe) and may require the use of the XL probe. Similarly, there is a separate probe for doing Fibroscan test in children (S probe).
Sometimes patients with NAFLD or fatty liver can have various other reasons which can falsely elevate the Fibroscan value which may not be truly representative of hepatic fibrosis. Hence the Fibrocan interpretation should be done by the treating doctor in the clinical context.
Estimation of liver fat with Fibroscan
Another advantage of Fibroscan is that, in addition to measuring fibrosis in the liver, it can simultaneously also measure the presence and severity of the fat in the liver by a built-in software called controlled attenuation parameter (CAP).
Other tests for liver fibrosis
In addition to Fibroscan, various blood tests and other elastography techniques are also available these days to assess the presence and extent of hepatic fibrosis in patients with NAFLD.