There are two common methods used for grading liver biopsy results: the Metavir and Knodell methods. Find out how these two methods are used in diagnosing liver diseases.
Liver biopsy is a surgical procedure wherein small tissue sample is taken from the liver so it can be examined with a microscope to diagnose liver disease or to estimate the degree of liver damage. It is often ordered by a doctor when a liver problem is difficult to diagnose with imaging techniques (e.g. ultrasound and x-ray) and serological tests.
Liver biopsies can be taken in three different approaches: via a needle through the skin (percutaneous liver biopsy), through the blood vessels (transvenous liver biopsy), or directly during abdominal surgery. For accurate diagnosis, the recommended size of tissue sample for laboratory examination should at least be 1.5 cm in length and 1.2-2 mm in diameter. The sample should also contain at least 6-8 portal triads.
In the laboratory, the sample is stained for easier examination under a microscope. All pertinent observations are recorded. Once all the needed data are obtained, the laboratory will use a grading system to report the results of liver biopsy to the doctor. Metavir and Knodell grading for liver biopsy results are commonly used by laboratories worldwide.
Metavir Grading for Liver Biopsy Results
The Metavir grading system uses two standardized numbers: one to indicate degree of inflammation (tissue swelling and irritation) and the other the degree of fibrosis (tissue scarring due to prolonged inflammation).
A 4-point scale is used in grading the degree of liver inflammation or histological activity:
- A0= no inflammation
- A1= mild inflammation
- A2= moderate inflammation
- A3= severe inflammation
A 5-point scale is used in grading the degree of liver fibrosis:
- F0= no fibrosis
- F1= minimal fibrosis
- F2= fibrosis has occurred and spread inside the areas of the liver including blood vessels
- F3= fibrosis is spreading and connecting to other liver areas that contain fibrosis
- F4= cirrhosis or advance liver fibrosis
Knodell Grading for Liver Biopsy Results
The Knodell grading system for liver biopsy results is more complex than the Metavir system. According to experts, Knodell score or HAI (histologic activity index) is much better in assessing the amount of liver inflammation or scarring. Knodell uses four categories in grading liver biopsy. The first three categories assess the amount of inflammation or necrosis present. These are the periportal or bridging necrosis, intralobular degeneration & focal necrosis, and portal inflammation. The fourth category measures the amount of fibrosis or scarring present. The scores or points given to each of the four categories are added to get the final score or the HAI. Below is the interpretation of the final score.
- 0= no inflammation present
- 1-4= minimal inflammation is present
- 5-8= mild inflammation is present
- 9-12= moderate inflammation is present
- 13-18= severe inflammation is present