Laboratory tests for Hepatitis B infection

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Different laboratory tests can diagnose hepatitis B virus (HBV) infection and monitor people with chronic hepatitis B. Hepatitis B is first diagnosed using a blood test that looks for certain antigens (fragments of HBV) and antibodies (produced by the immune system in response to HBV). Initial blood tests to diagnose HBV infection look for one antigen, HBsAg (hepatitis B surface antigen), and two antibodies, anti-HBs (antibodies to the HBV surface antigen) and anti-HBc (antibodies to HBV core antigen).
Actually, two types of anti-HBc antibodies are produced: immunoglobulin M (IgM) antibodies and immunoglobulin G (IgG) antibodies. IgM antibodies are produced early in the course of infection. IgG antibodies are produced later in the course of infection and replace IgM antibodies.
Depending on the results of the above tests, additional diagnostic tests may be necessary. Somebody who has never been infected with HBV or has been vaccinated against the virus does not require any additional testing. Someone who was recently infected with HBV and has acute hepatitis B may want to get another blood test after six months have passed to make sure that the necessary immune response has occurred. People with chronic HBV infection require additional testing to learn more about their hepatitis B.
Additional tests
HBeAg and anti-HBe: HBeAg is the hepatitis B envelope antigen, and anti-HBe are the antibodies produced against this antigen. If HBeAg is detectable in a blood sample, this means that the virus is still active in the liver (and can be transmitted to others). If HBeAg is negative and anti-Hbe is positive, this generally means that the virus is inactive. However, in some people with chronic hepatitis – specially those who have been infected with HBV for many years – may have what is known as a “precore” or “core variant” mutated form of HBV. This can cause HBeAg to be negative and anti-HBe to be positive, even though the virus is still active in the liver.
HBV viral load: This test measures the actual amount of HBV in a blood sample, which helps determine whether HBV is reproducing in the liver. In a person with detectable HBeAg, an HBV viral load greater than 20,000 international units per millilitre (IU/mL) of blood indicates that the virus is active and has the greatest potential to cause damage to the liver. Similarly, in a person with an active HBeAg-negative chronic hepatitis B, an HBV viral load of greater than 2,000 IU/mL indicates that the virus is active and has potential to cause damage to the liver. Measurement of HBV viral load is of help in monitoring of treatment response.
Liver Function Tests: One of the most important liver enzymes to look for is alanine aminotransferase (ALT), sometimes called SGPT on lab reports. An elevated ALT level indicates that the liver is not functioning properly and that there is a risk of permanent liver damage. During acute hepatitis B infection, ALT levels can be temporarily elevated, but this rarely leads to long-term liver problems. In chronic hepatitis B, ALT levels can be either periodically or consistently increased, indicating a higher risk of long-term liver damage.
HBV genotype: HBV genotypes and subgenotypes have been associated with differences in clinical and virological characteristics, indicating that they may play a role in the virus-host relationship. The HBV genotype appears to influence not only the natural history of HBV related liver disease but also the response to HBV treatment. HBV genotype also determine the treatment regime and duration of treatment.
Imaging: HBV infection is a known cause of liver cancer. Magnetic resonance imaging (MRI) and “triple-phase” computed tomography (CT or CAT) scans are becoming more common, less painful tests to look for changes in the liver, most notably liver cancer.
Some experts suggest that MRI and triple-phase CT scans are the best way to look for tumours in people who have cirrhosis of the liver.
Ultrasound: Like MRI and CT scans, ultrasound can be used to look for liver cancer tumours. Some experts suggest that ultrasound is an effective screening tool in people who do not have cirrhosis of the liver.
Fibroscan: Fibroscan, also called transient elastography, is a technique used to assess liver stiffness (measured in kPa correlated to fibrosis) without invasive investigation. The result shows the condition of the liver and allows physicians to diagnose and monitor disease evolution in conjunction with treatment and other factors. It helps to anticipate various complications, as well as assess and monitor the damage caused by complications such as cirrhosis.
Liver biopsy: Sometimes a liver biopsy may be needed to look for evidence of cirrhosis and liver cancer.
(The writer is Junior Microbiologist, BABINA Diagnostics, Imphal)

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