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Christine M. Kukka
HBV Project Manager
To find out if you are infected with hepatitis B, or the status of your infection, a healthcare worker will take a blood sample from you and a laboratory will analyze it for several hepatitis B viral components that provide a roadmap to your hepatitis B infection.
These viral components include antigens or proteins that make up different parts of the hepatitis B virus (called HBV), and antibodies, which your immune system generates to combat each antigen.
A viral test is different than a “liver function” test, which also requires a blood sample. Liver function tests look for liver enzymes, such as alanine aminotransferase or ALT, and other substances that indicate if liver cells are healthy or damaged.
To overcome a hepatitis B infection, the immune system must produce antibodies against all HBV antigens.
• The outer coating of the virus is made up of the surface antigen or HBsAg. It surrounds the core of the virus.
• The inner shell contains the core antigen (HBcAg).
• Another antigen found in the core’s interior is the “e” antigen (HBeAg).
• Also within the core of the virus are the viral DNA genetic material and the DNA polymerase enzyme, which contains the key genetic replication instructions.
Doctors look for surface antigens and antibodies, the “e” antigens and antibodies, and core antibodies in a viral test. They should also look at the levels of virus in the blood (the hepatitis B DNA or HBV-DNA) to track how actively viruses are replicating in your liver.
Hepatitis B Surface Antigen (HBsAg): The presence of surface antigen in your lab report indicates you have a hepatitis B infection. It can be an acute (short-term) or a chronic (potentially life-long) infection. Simply put, if you have surface antigen, you have hepatitis B and are capable of infecting others.
When HBV replicates in the liver, it produces more surface antigen than is needed to generate new viruses. The excess surface proteins clump together in the bloodstream and are easily identified in lab tests.
Laboratory tests can usually identify surface antigen about four weeks after infection, but it can take up to 12 weeks after infection for a test to reveal the presence of surface antigen.
In an acute infection, the immune system is able to combat the “foreign” surface antigen and create surface antibodies (HBsAb or anti-HBsAg) to vanquish the infection within four months of when symptoms first appear. However, in a chronic infection, the immune system cannot mount a successful campaign to rid the body of the surface antigen and create enough surface antibodies to keep the infection away. Chronic hepatitis B is diagnosed when surface antigen is present in the bloodstream for more than six months.
When surface antigens disappear and surface antibodies appear in a lab report, then the person is considered cured. Bottom line: the surface antibody is what everyone wants to achieve. It means they are cured and can no longer infect others.
Hepatitis B Core Antigen (HBcAg) and Antibodies (anti-HBc or HBcAb): The hepatitis B core antigen forms the inner core of the virus and is produced when the virus replicates in liver cells. The core antigen is found only in HBV-infected liver cells, not in the bloodstream. But hepatitis B core antibodies are found in the bloodstream and can be identified by viral tests.
Core antibodies are the first detectable HBV antibodies to appear, usually around eight weeks after infection. They are present in anyone who has had either an acute or a chronic HBV infection.
People who have been vaccinated against hepatitis B have been injected with only the surface antigen portion of the virus, to cause their immune systems to produce surface antibodies to forever protect them against infection. A viral test on their blood would only reveal the surface antibody. However, anyone who has been actually infected with HBV would show both core antibodies as well as surface antibodies in their lab test.
Hepatitis B “e” Antigen (HBeAg) and “e” Antibodies (anti-HBe or HBeAb): The “e” antigen is a protein secreted into the bloodstream by viruses that are actively replicating in liver cells. When a lab test finds “e” antigen, it means the virus is actively replicating and that the person usually has a large quantity of HBV-DNA in their bloodstream. They are usually more infectious to anyone who may come into contact with their blood or body fluids, than someone who has developed the “e” antibody.
People with the “e” antigen are considered at greater risk of progressing to liver disease than those who have developed an “e” antibody because it indicates ongoing viral replication in the liver. Children with chronic hepatitis B often test positive for the “e” antigen because their immune systems have not yet “noticed” the virus, or attempted to stop the virus from replicating in the liver.
In some unique cases, particularly in people with certain HBV genotypes or viral strains, there are hepatitis B viruses that can replicate without producing the “e” antigen. This type of HBV infection is called “e” antigen negative hepatitis B. Someone with this type of HBV infection (called a precore mutation) can still produce the “e’ antibody.
In acute cases of hepatitis B, when the body’s immune system quickly responds and eradicates the viral infection, the “e” antigen appears only briefly. It disappears as viral replication declines in the liver as the immune system launches “e” antibodies to combat this antigen.
Hepatitis B “e” antibodies usually persist for one or more years after resolution of an acute infection. Sero-conversion, or production of “e” antibodies, is the goal of most medical treatments for hepatitis B today. Once the “e” antibody is produced, there are usually fewer viruses infecting and damaging the liver.
Hepatitis B Virus DNA (HBV-DNA): HBV-DNA is the genetic material that carries the blueprint of the virus. It is found in the bloodstream and is the best indication of how rapidly the virus is replicating in the liver. High levels of HBV-DNA, up to several billion viral particles per milliliter, indicate rapid viral replication in the liver. Low or undetectable rates indicate an “inactive” infection, with low viral replication in the liver.
Increasingly, more and more doctors are testing patients’ HBV-DNA levels. But this is a relatively new and very costly lab test. Some insurance companies may not cover it unless the test is used to monitor medical treatment. Patients must be assertive and proactive in asking for this test, which is also very useful if someone has “e” antigen negative hepatitis, because it will show active viral replication despite the absence of the “e” antigen.
The World Health Organization has recently created an international standard for measuring HBV-DNA in lab tests. It established the HBV-DNA international unit (IU or viral copies) per milliliter (mL). But not all labs in the United States and Canada have accepted and use this global standard yet. However, even if a lab doesn’t use that standard, it should be able to convert a patient’s HBV-DNA results into viral copies per milliliter or IU/mL.
The National Institutes of Health have suggested that viral loads that exceed 105 copies/mL (100,000 viral copies per milliliter) be considered ‘clinically significant’ viral loads, while lower viral loads represent a relatively inactive infection.
“However, there are problems with this definition,” wrote Drs. Anna Lok and Brian McMahon in the American Association for the Study of Liver Diseases Practice Guidelines published in October 2002. “First, assays (tests) for HBV-DNA are not well standardized. Second, some patients with chronic hepatitis B have fluctuating HBV-DNA levels that may at times fall below 105 copies/mL. Third, the threshold HBV-DNA level that is associated with progressive liver disease is unknown.”
Except for HBV-DNA, all antigen and antibody test results are reported as either positive or negative. Either the antigens or antibodies are discernable at a certain level, or they are undetectable. Only the HBV-DNA test result is reported numerically.
Recently, medical researchers have begun to examine what impact HBV genotypes or viral strains have on a patient’s infection progression and response to treatment. However, to date tests to determine genotype have been performed only by research centers. However, officials expect in the years ahead that genotyping will become part of a patient’s viral lab test.
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