Rapid tests for hepatitis b
Hepatitis B viral components
Hepatitis B DNA (HBV DNA)
Hepatitis B DNA and Hepatitis B DNA polymerase are the first viral components that can be detected in the bloodstream after initial infection. It can be detected as early as 1 week after infection. HBV DNA is assayed using PCR which is expensive, equipment intensive, and technically difficult to perform. Testing for HBV DNA (and HBV polymerase) is generally rare since other Hepatitis B markers to measure viral load or exposure are cheap, common and effective.
Hepatitis B surface antigen (HBsAg)
The surface antigen is composed of the proteins that coat the outer layer of the hepatitis B virus. After infection and 1 to 6 weeks before symptoms occur HBsAg appears. If this test is positive, then the hepatitis B virus is present. This refers to the outer surface of the hepatitis B virus that triggers an antibody response. A positive test for the presence of hepatitis B surface protein (HBsAg), is the standard used to indicate active infection with hepatitis B. If HBsAg is present for more than 6 months this is generally taken to indicate chronic infection. Infected people can pass the virus on to others.
Hepatitis B surface antibody (HBsAb)
The surface antibody is formed in response to the hepatitis B virus Surface Antigen. This antibody is present if the patient has been exposed to the HBsAg from a prior hepatitis B infection and cleared the virus, or if they have been vaccinated. When a patient is positive for the HBsAb their immune system has successfully developed a protective antibody against the hepatitis B virus. Recovery from infection is diagnosed by determining no HBsAg is found in the blood and the Hepatitis B Antibody (HBsAb) is present. The HBsAb antibody provides long-term protection against future hepatitis B infection. There test to find this antigen.
Hepatitis B core antigen (HBcAg)
There are a number of immunological test to detect this antigen but its clinical significance is of a positive result is dependent on the out come of one or more other antigen or antibody tests.
Hepatitis B core antibody (HBcAb or anti-HBc)
This refers to an antibody that is produced in response to the core-proteins. The core proteins protect the DNA of the hepatitis B virus. This antibody does notprovide any protection against the hepatitis B virus since it is covered in the surface antigen proteins. These antibodies to appear around 4-8 weeks after an infection with HBV. A positive HBcAb test indicates only that a person has been exposed to the hepatitis B virus but tells little more. In patients that are chronically infected with hepatitis B, the HBcAb usually is present, along with the Hepatitis B Surface Antigen (HbsAg). A positive HBcAb test along with a positive surface antibody (HBsAb) indicates prior infection and recovery. A vaccinated person that is exposed to HBV may also test positive HBcAb test.
The HBcAb assay is often used to screen blood donations, but as noted above it cannot be used alone to make a diagnosis.
Hepatitis e antigen (HBeAg or HBe)
It must be noted that not all strains of HBV have the Hepatitis 'e' antigen (HBeAg).
The HBeAg is a peptide and normally detectable in the bloodstream when the hepatitis B virus is actively reproducing. Antibodies against the HBeAg are detectable about 4 months after infection. HBeAg is distinct from the HBsAg and the HBcAg . HBeAg is an antigen, or possibly a group of antigens, that is associated with the viral nucleocapsid. The function, if any, of this non structural protein is unknown and it is not required for the virus to properly replicate. Its presence indicates that the virus is actively replicating and the individual is potentially infectious. HBeAg is only transiently present in acute infections while in chronic infection its presence indicates that HBV is still actively reproducing and reflects a worse prognosis.
There is data to indicate that the HBe protein may be influential in level of the immune systems response to HBV infection. HBV viruses lacking the HBeAg are more aggressive and demonstrate much more severe pathology, even with a lower viremia.
The HBeAg is generally detectable at the same time as HBsAg and disappears before HBsAg disappears.
Hepatitis e antibody (HBeAb or anti-HBe)
Antibodies to HBeAg are labeled as HBeAb. These normally appear 2-4 weeks after HBeAg is no longer detectable and their presence reflects a favorable prognosis. HBeAb’s can persist for years, but usually disappears earlier than HBsAbs or HBcAb’s. Anti-HBe should not be regarded as the sole serologic marker for hepatitis B infection.
If a patient was infected with a strain that did not contain the HBeAg gene, they will not develop the HBeAb.
