Hepatitis B should be suspected in cases where a person has been in contact with blood or bodily fluids from an infected individual and is presenting with symptoms of hepatitis.
An outline of how hepatitis B is diagnosed is given below:
- The blood is tested for viral antignes or for antibodies the body produces against the virus. For hepatitis B, the first viral antigen to present during infection is the hepatitis B surface antigen (HbsAg). However, during early infection, this antigen may not be present and it can also be undetectable later in infection, when it may have been cleared by the host.
- The virus also contains an inner core particle that encases the viral genome. This core particle contains either 180 or 240 copies of core protein, also called hepatitis B core antigen, or HBcAg. During a period of time while the host is infected but is clearing the virus, IgM antibodies that are specific to this HbcAg may be the only sign that the infection is present. Therefore, panels used to detect hepatitis B usually contain HbsAg and total anti-HBc (IgM and IgG).
- The presence of HbsAg is shortly followed by the appearance of another antigen called hepatitis B e antigen (HBeAg). During the natural course of infection, this antigen is cleared by the immune system and the anti-HBe or antibodies immediately start to rise.
- A liver function test may be carried out to measure the levels of specific enzymes and protein in the blood that act as indicators of liver damage.
- An abdominal ultrasound scan may also be performed to assess the liver.
- Polymerase chain reaction (PCR) tests are available to determine the amount of hepatitis B virus DNA in the blood (the viral load). These can be used to establish a patient’s infection status and to monitor treatment.
Reviewed by Sally Robertson, BSc