2.01 Serological tests
Thu, 23 Feb 2012
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2.01 Serological tests

Hepatitis B virus antigens and antibodies

An antigen (Ag) is a substance that can elicit an immune response (e.g. formation of antibodies) in a host.  Antibodies are proteins known as immunoglobulins (Ig) which are designed to recognise and bind to antigens (Eales, 2003).

Both antigens and antibodies are important in serological tests for hepatitis B virus infection.  There are three hepatitis B virus antigens and they each have corresponding antibodies.

HEPATITIS B VIRUS ANTIGENS AND ANTIBODIES

Antigens

Antibodies

HBsAg hepatitis B 's' or surface antigen (envelope protein of virion) 

Anti-HBs (also known as HBsAb or 'surface antibody') antibody to HBsAg

HBcAg - hepatitis B 'c' or core antigen (nucleocaspid of virion)

Anti-HBc (also known as HBcAb or 'core antibody') -  antibody to HBcAg. Two classes of Anti-HBc:·

  •  Anti-HBc IgM
  •  Anti-HBc IgG

HBeAg - hepatitis B 'e' antigen (water-soluble form of core protein - secreted by cells infected with hepatitis B virus) 

Anti-HBe (also known as HBeAb or 'e antibody) - antibody to HBeAg

Sources: Tibbs and Smith (2001); Timbury et al (2002); World Health Organization (2002)


Serological markers in acute and chronic hepatitis B infection

With one exception, all the serological markers (indicators) for hepatitis B virus infection are hepatitis B virus antigens or their corresponding antibodies. The one exception is hepatitis B viral DNA.  These markers are used to diagnose and monitor the progression of hepatitis B virus infection.

SEROLOGICAL MARKERS IN ACUTE AND CHRONIC HEPATITIS B VIRUS INFECTION

SEROLOGICAL MARKERS ACUTE INFECTIONCHRONIC INFECTION GENERAL NOTES

HBsAg
(surface antigen)

  • Can be detected for several weeks before symptoms of acute infection.
  • Present during acute infection.
  • It is always present in chronic infection.
  •  Indicates person is potentially infectious.
  •  Useful for diagnosis of HBV infection.
  • Used in vaccines to elicit a protective antibody response.
     
HBeAg (e antigen) 
  • Detectable in early phase of hepatitis B virus infection, shortly after surface antigen appears.
  • At this early stage it indicates an active acute infection, at its most infectious period. 
  • Positivity in chronic infection is always associated with high levels of virus. 
  • Treatment for e antigen positivity aims to convert to e antigen negativity.
Anti-HBs (surface antibody) 
  • Appearance 1-4 months after start of symptoms indicates recovery and subsequent immunity to hepatitis B virus infection.
  •  In people who are recovering from acute hepatitis B virus infection, surface antibody usually appears after surface antigen has disappeared.   
  • Is never detectable in chronic infection.
  • Can neutralise hepatitis B virus.
  • Protects against reinfection. 
  • Marker of immunity against hepatitis B virus (is used to assess response to vaccination).

Anti-HBc (core antibody)

(anti-HBc IgM and anti-HBc IgG)

  • Usually anti-HBc IgM indicates recent infection.
  • Appears soon after surface antigen and may be only marker of infection in 'window period' after surface antigen disappears and before surface antibody appears. 
  • Anti-HBc IgG is always present in chronic infection.
  • Anti-HBc IgM is not present. 

  • Core antigen (HBcAg) is not detectable in serum so is detected indirectly via presence of core antibody.
  • Anti-HBc indicates past or present infection i.e. the person has been in contact with the virus.
  • Anti-HBc testing identifies all previously infected people but does not differentiate between carriers and non-carriers.

Anti-HBe (e antibody)
  • Indicates infection is likely to resolve spontaneously.
  • In chronic infection its presence usually (but not always) indicates that the level of virus is likely to be low. 
  • Transition from e antigen to e antibody positivity usually indicates that virus production has decreased significantly.
  •  But e antibody may be associated with low or high viral DNA levels (usually low).
  • If you have e antibody positivity with high viral DNA levels, you are likely to require treatment.
HBV DNA 
  • Detectable as soon as 1 week after initial infection (but not routinely measured in acute hepatitis B virus infection).  
  • An important indicator of the level of viral replication.
  • Used to identify patients who may need treatment.
  • Used for monitoring patient's response to antiviral treatment. 

  • Indicates the presence of circulating complete viruses (always infectious).
  • High levels do not necessarily equate with liver damage, but significant ongoing damage will not be observed in the context of low levels.

Sources: Tibbs and Smith (2001); World Health Organization (2002); Hepatitis B Foundation (US) (not dated); Lok and McMahon, 2007)

Summary of some commonly used hepatitis B virus tests

Here's a summary of some commonly used serological tests.

INTERPRETATION OF SOME COMMON HEPATITIS B VIRUS TESTS

TESTS

RESULTS

INTERPRETATION

HBsAg

Anti-HBs

Anti-HBc

Negative

Negative

Negative

Has no natural or acquired immunity
against hepatitis Bvirus infection and
is susceptible to this infection.

HBsAg

Anti-HBs

Anti-HBc

Negative

Positive

Positive

Has had hepatitis B virus infection and
 acquired immunity.

HBsAg

Anti-HBs

Anti-HBc

Negative

Positive

Negative

Is immune as a result of hepatitis B
vaccination.

HBsAg

Anti-HBs

Anti-HBc

Anti-HBc IgM

Positive

Negative

Positive

Positive

Has acute hepatitis B virus infection.

HBsAg

Anti-HBs

Anti-HBc

Anti-HBc IgM

Positive

Negative

Positive

Negative

Has chronic hepatitis B virus infection.

Source: Adapted from Centers for Disease Control and Prevention (2006)
Laboratory detection of serological markers

Laboratory detection of serological markers

Detection of hepatitis B virus antigens and antibodies
Laboratory detection of antibodies is usually based on enzyme-linked immunosorbent assay (abbreviated to ELISA or EIA).  ELISA is also adapted to detect antigens (Timbury et al, 2002).

Tests for hepatitis B virus antigens and antibodies are simple, automated, inexpensive and readily available.  Results can be quick e.g. it is possible to obtain an HBsAg result in a day.

Detection of hepatitis B viral DNA
The polymerase chain reaction (PCR) is used to detect viral DNA.  PCR can be adapted to quantify viral DNA (i.e. to measure the level of circulating viruses).  The branched DNA (bDNA) is another test used to quantify viral DNA (Timbury et al, 2002).

Testing for HBV DNA is not routine and is expensive.  It takes about a week to get the results.

Serological tests in context

Tables showing interpretation of serological test results are useful but it's important to recognise that these tests always need to be interpreted in context: for example, the reason for the hepatitis B virus tests, the patient's age and state of health and whether he or she has had any other investigations, such as liver function tests.  Furthermore, concentrations (titres) of serological markers vary at different stages of hepatitis B virus infection.  All of these factors need to be taken into account when clinical decisions are made.  If you have hepatitis B virus infection you are therefore advised to discuss your serological test results with a health care professional who is familiar with your medical history and clinical condition.

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Created on 09/12/2010

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