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Introduction:
HBsAg is one of the earliest markers that appear in the blood following infection with Hepatitis B virus (HBV). This infection of the liver is transmitted by homosexual or heterosexual activity, blood borne exposure, mother - infant, close personal contact and by intake of contaminated water and food products. In the HBV infected people, the virus persists for the rest of their lives and can be passed on to others. Therefore Hepatitis B has become a global public health problem.
Infection with HBV results in the appearance of a number of serological markers and one of the first of such markers is Hepatitis B surface antigen (HBsAg). The HBV infection causes a wide variety of liver damages such as acute self-limiting infection, fulminating hepatitis, chronic hepatitis with progression to cirrhosis and liver failure, and a symptomatic chronic carrier state.
Hepatitis B surface antigen (HBsAg) appears 1-7 weeks before biochemical evidence of liver disease or jaundice. Three weeks after the onset of acute hepatitis almost half of the patients will still be positive for HBsAg. In the chronic carrier state, the HBsAg persists for long periods (6-12 months) with no seroconversion to the corresponding antibodies. Therefore, screening for HBsAg is highly desirable for all donors, pregnant women and people in high-risk groups.
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BACKGROUND:
The discovery of Australian antigen by Blurnberg et al., and its subsequent identification as the surface antigen of hepatitis B virus (HBsAg) represents a significant break-through in the understanding of serum hepatitis. It is known that the screening of blood donor for the presence of this antigen in serum has significantly reduced the incidence of hepatitis B in blood transfusion recipients. The chemical composition of the HBsAg consists of lipid, carbohydrate and protein. The protein moiety of HBsAg contains several polypeptides ranging from 23,000 to 97,000 Dalton in molecular weight. The antigenic determinant on the protein moiety of HBsAg determines the specific characteristics of the different serotypes of the virus and is the basis for this immunoassay. Sero-types of HBsAg are of the a type (al, a2, and a3) and also of the d/y type(1d/y, 2d/y, 3d/y) and the w/r type. The following combinations are possible: adw, adr, ayw, and ayr. HBsAg EIA is a qualitative enzyme Immunoassay for the detection of HBsAg in human serum or plasma. The assay should detect all serotypes of HBsAg.
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