Hepatitis B is an infection of the liver caused by the hepatitis B virus (HBV), a double-stranded DNA virus of the Hepadnaviridae family that replicates by reverse transcription.
Hepatitis B is the most common cause of hepatitis globally, and the World Health Organization (WHO) recently estimated that more than 350 million people worldwide are chronically infected with HBV. Areas with a high prevalence of HBV infection include sub-Saharan Africa, most of Asia and the Pacific islands. IN these areas it is estimated that greater than 10% of the population have chronic HBV infection. In the UK the prevalence is much lower, with only around 1 in 350 people thought to have chronic HBV infection.
The diagnosis of HBV infection is established via serological testing. The diagnostic panel for hepatitis B serology enables us to determine susceptibility to infection, the presence of acute or chronic infection, and immunity through vaccination or past infection. This panel usually involves testing for:
- Hepatitis B surface antigen (HBsAg)
- Hepatitis B surface antibody (anti-HBs)
- Hepatitis B core antibody (anti-HBc)
- IgM antibody to hepatitis B core antigen (IgM anti-HBc)
Hepatitis B serology
Hepatitis B surface antigen (HBsAg) is a protein on the surface of the HBV. It can be detected in high levels in serum during acute or chronic HBV infection. The presence of HBsAg indicates that the person is infectious. The body usually produces antibodies to HBsAg as part of the normal immune response to infection. HBsAg is the antigen used to make hepatitis B vaccine.
Hepatitis B surface antibody (anti-HBs) indicates recovery and immunity from the HBV infection. Anti-HBs also develops in a person who has been successfully vaccinated against hepatitis B.
Total hepatitis B core antibody (anti-HBc): Appears at the onset of symptoms in acute hepatitis B and persists for life. The presence of anti-HBc indicates previous or ongoing infection with the HBV in an undefined time frame. It is not present following hepatitis B vaccination.
IgM antibody to hepatitis B core antigen (IgM anti-HBc) indicates recent infection with HBV (<6 months). Its presence indicates acute infection.
The following table summarises the presence of hepatitis B markers according to each situation:
| Marker | Result | Situation |
|---|---|---|
| HBsAg Anti-HBc Anti-HBs | Negative Negative Negative | Susceptible to infection |
| HBsAg Anti-HBc Anti-HBs | Negative Positive Positive | Immune due to natural infection |
| HBsAg Anti-HBc Anti-HBs | Negative Negative Positive | Immune due to vaccination |
| HBsAg Anti-HBc Anti-HBs IgM anti-HBc | Positive Positive Negative Positive | Acute infection |
| HBsAg Anti-HBc Anti-HBs IgM anti-HBc | Positive Positive Negative Negative | Chronic infection |
Hepatitis B vaccination
Hepatitis B vaccines are prepared from the viral surface antigen. The recombinant vaccine is now the most widely used vaccine and induces a sufficient antibody response in 90% of individuals.
Indications for hepatitis B vaccination include:
- All health care professional’s working in the UK
- Other professions with occupational risks (foster carers, staff of custodial institutions, morticians etc.)
- Babies of mothers with hepatitis B during pregnancy
- Close family contacts of a case or carrier
- IV drug abusers
- Individuals with haemophilia
- Individuals with chronic renal failure
- Sex workers and individuals with frequently changing sexual partners
The vaccines should be stored between 2-8°C, as freezing destroys its efficacy. The vaccine is administered intramuscularly, either into the deltoid region (preferred) or anterolateral thigh. The buttock should be avoided as it reduces the efficacy of the vaccine.
The standard regime is to give three doses of the vaccine, the 1st and 2nd one month apart and the 2nd and 3rd six months apart. Antibody titres should be tested 2 to 4 months after the primary course.
A peak titre above 100 mIU/ml is regarded as a good response and implies long-term immunity. A peak titre between 10-100 mIU/ml is considered to be a low response, and a peak titre of less than 10mIU/ml is regarded as a poor response.
The presence of the Australia antigen indicates current HBV infection. The Australia antigen is the surface antigen of the Hepatitis B virus (HBsAg).
Header image used on licence from Shutterstock
Thank you to the joint editorial team of www.mrcgpexamprep.co.uk for this exam tips post.
