Hepatitis B: Hepatitis B tests

What are tests for Hepatitis B?

Infection with hepatitis B is suspected when the medical history and the physical examination reveal risk factors for the infection or symptoms and signs that are suggestive of hepatitis B. Abnormalities in the liver tests (blood tests) also can raise suspicion; however, abnormal liver tests can result from many conditions that affect the liver. The diagnosis of hepatitis B can be made only with specific hepatitis B virus blood tests. These tests are known as hepatitis ‘markers’ or ‘serology.’

Markers found in the blood can confirm hepatitis B infection and differentiate acute from chronic infection. These markers are substances produced by the hepatitis B virus (antigens) and antibodies produced by the immune system to fight the virus. Hepatitis B virus has three antigens for which there are commonly-used tests – the surface antigen (HBsAg), the core antigen (HBcAg) and the e antigen (HBeAg).

  • HBsAg and anti-HBs

The presence of hepatitis B surface antigen (HBsAg) in the blood indicates that the patient is currently infected with the virus. HBsAg appears an average of four weeks after initial exposure to the virus. Individuals who recover from acute hepatitis B infections clear the blood of HBsAg within approximately four months after the onset of symptoms. These individuals develop antibodies to HBsAg (anti-HBs). Anti-HBs provide complete immunity to subsequent hepatitis B viral infection. Likewise, individuals who are successfully vaccinated against hepatitis B produce anti-HBs in the blood.

Patients who fail to clear the virus during an acute episode develop chronic hepatitis B. The diagnosis of chronic hepatitis B is made when the HBsAg is present in the blood for at least six months. In chronic hepatitis B, HBsAg can be detected for many years, and anti-HBs do not appear.

  • Anti-HBc antibody:

In acute hepatitis, a specific class of early antibodies (IgM) appears that is directed against the hepatitis B core antigen (anti-HBc IgM). Later, another class of antibody, anti-HBc IgG, develops and persists for life, regardless of whether the individual recovers or develops chronic infection. Anti-HBc IgM can be used to diagnose an acute hepatitis B infection.

  • HBeAg, anti-HBe, and pre-core mutations

Hepatitis B e antigen (HBeAg) is present when the hepatitis B virus is actively multiplying, it shows infectivity. Whereas the production of the antibody, anti-HBe, (also called HBeAg seroconversion) signifies a more inactive state of the virus and a lower risk of transmission.

In some individuals infected with hepatitis B virus, the genetic material for the virus has undergone a structural change, called a pre-core mutation. This mutation results in an inability of the hepatitis B virus to produce HBeAg, even though the virus is actively reproducing. This means that even though no HBeAg is detected in the blood of people with the mutation, the hepatitis B virus is still active in these persons and they can infect others.

  • Hepatitis B virus DNA

The best marker of hepatitis B virus reproduction is the level of hepatitis B virus DNA in the blood. Detection of hepatitis B virus DNA in a blood sample indicates that the virus is actively multiplying. In acute hepatitis, HBV DNA is present soon after infection, but is eliminated over time in patients who clear the infection. In chronic hepatitis, levels of HBV DNA often continue to be elevated for many years and then decrease as the immune system controls the virus. HBV DNA levels are sometimes referred to as the ‘viral load’.

  • How is the hepatitis B blood tests interpreted?

The following table gives the usual interpretation for sets of results from hepatitis B blood (serological) tests.

Most Likely Status*

Tests

Results

Susceptible, not infected, not immune HBsAg
anti-HBc
anti-HBs
negative
negative
negative
Immune due to natural infection HBsAg
anti-HBc
anti-HBs
negative
positive
positive
Immune do to hepatitis B vaccination HBsAg
anti-HBc
anti-HBS
negative
negative
positive
Acutely infected HBsAg
anti-HBc
IgM anti-HBc
anti-HBs
positive
positive
positive
negative
Chronically infected HBsAg
anti-HBc
IgM anti-HBc
anti-HBs
positive
positive
negative
negative

*Interpretation of the hepatitis B virus blood tests should always be made by an experienced clinician with knowledge of the patient’s medical history, physical examination, and results of the standard liver blood tests.

If a patient has had a large amount of vomiting or has not been able to take in liquids, blood electrolytes may also be checked to ensure that the patient’s blood chemistry is in balance.

Other tests may be needed to rule out other medical conditions.

X-rays and other diagnostic images are needed only in very unusual circumstances.

If a patient is diagnosed with chronic hepatitis B, they will need to visits to their health care practitioner regularly. Blood tests can help determine how active the infection is and whether there has been damage to the liver.

Blood tests alone may not be enough to guide treatment in chronic HBV. Other tests include:

  • CT scan or ultrasound:

These tests are used to detect the extent of liver damage and may also detect cancer of the liver caused by chronic hepatitis B.

  • Liver biopsy:

This involves removal of a tiny piece of the liver. It is usually done by inserting a long needle into the liver and withdrawing the tissue. The tissue is examined under a microscope to detect changes in the liver. A biopsy may be done to detect the extent of liver damage or to evaluate how well a treatment is working.

 

What is the role of a liver biopsy in chronic hepatitis B?

During a liver biopsy, a small sample of liver tissue is collected and examined under the microscope. This test is valuable because this sample reflects the health of the liver. It can show the amount of liver injury (inflammation or cirrhosis). Liver biopsy is not needed to diagnose hepatitis B, but it is used for monitoring the progression of liver damage in people with chronic hepatitis and helping to choose or evaluate treatment options.

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