Diagnosis and monitoring

Blood tests can detect the presence of hepatitis B virus antigen and antibodies, which show whether an individual has been exposed to the virus. Antigens are foreign proteins or substances in the body, and antibodies are proteins produced by the immune system in response to antigens.

People who have successfully cleared the virus are left with antibodies against it. If fragments of the virus itself, called hepatitis B surface antigen (HBsAg), are found in the blood for more than six months, the person is a chronic carrier and capable of infecting others. People with chronic infection are sometimes also positive for hepatitis B e antigen (HBeAg), which indicates that the virus is actively replicating. However, some people are infected by a mutant precore form of the virus known as HBeAg-negative that does not produce this antigen, and appears to be harder to treat. Some people with chronic hepatitis C may be co-infected with hepatitis B but lack detectable hepatitis B virus surface antigen.¹ In addition, some HIV-positive people, especially if they also have hepatitis C, may not show either HBV surface antigen or surface antibodies, but may still have hepatitis B virus core antibodies, which the immune system produces to fight the virus.² This is called an occult infection, and its clinical significance is not known.

There are also tests that measure hepatitis B virus's genetic material, or DNA, in the blood. These viral load tests may detect DNA even if antibodies and antigens are not detectable. These tests are used to tell how well anti-hepatitis B treatment is working.

After a diagnosis of chronic infection, regular monitoring of the liver is advised. Blood tests including liver function tests should be conducted at least every six to 12 months. A liver function test measures levels of particular proteins or enzymes, including alanine aminotransferase (ALT) and aspartate aminotransferase (AST) in the blood to determine how well the liver is working. See Liver function in A to Z of tests for further details. If a patient already has cirrhosis, a liver ultrasound may be conducted every six months to screen for signs of liver cancer. A liver biopsy may also be performed to determine the extent of liver damage.

United Kingdom guidelines recommend that all HIV-positive patients should be tested for markers of hepatitis B infection within a month of their HIV diagnosis. Those without evidence of infection should be vaccinated against the virus, and should also receive vaccinations for hepatitis A. Liver function should be regularly checked in co-infected people who have had exposure to the hepatitis B virus.

The guidelines also recommend that:

• Babies born to mothers with hepatitis B virus should be vaccinated against the virus at birth and receive post-exposure prophylaxis with injected HBV antibodies or immunoglobulin.

• HIV / hepatitis B virus co-infected patients should be counselled about the potential dangers of alcohol consumption, which can accelerate liver damage, and about ways of reducing the risk of hepatitis B virus transmission. Sexual and household contacts should be tested for HBV, and vaccination is suggested.

• Patients with cirrhosis should be screened for liver cancer, and anti-hepatitis B therapy should be considered for people with active viral replication and raised liver enzyme levels. However, the best time to start therapy has not been determined.