Hepatitis B virus surface antigen (HBsAg)

Hepatitis B virus Consists of a nucleus and a membrane. Its genome contains double-stranded DNA. The infection is transmitted through blood or sexual contact. Incubation period - about 70 days (40-160 days). The virus is also found in other body fluids, such as saliva. It can be passed from mother to baby through contact with blood or vaginal secretions, but it is considered impossible to pass it through the placenta.

Hepatitis B virus surface antigen (HBsAg) Is part of the outer membrane of the virus. It is known as the "Australian Antigen" and is one of the first markers to appear in the blood at the end of the incubation period (in parallel with the detection of viral DNA in the blood) and 2 weeks before the appearance of HBcor-IgM (antibody to hepatitis B antigen). Its disappearance is a favorable prognostic criterion and, conversely, its persistence for more than 6 months indicates the chronicity of the process.

Normally, elimination of HBsAg is observed after normalization of ALT and disappearance of clinical manifestations.

In response to this antigen, the body produces protective antibodies (Anti-HBs), which are detected 1-4 months after the elimination of HBsAg (this period is called the "serological window" period) and their appearance indicates recovery. The appearance of these antibodies in parallel with the detection of HBsAg is an unfavorable prognostic criterion (observed in fulminant hepatitis).

In the chronic course of hepatitis B, HBsAg is constantly detected, although it does not show replication activity (it is necessary to detect the DNA of the causative agent by PCR, determination of HBeAg and antibodies) and can remain in the body for life. About 5-10% of adults and 90% of children infected by the mother are unable to get rid of the virus and remain a chronic carrier of HBsAg. One-third of patients who carry HbsAg develop chronic hepatitis, which over time can progress to cirrhosis of the liver and in some cases may even lead to hepatocellular carcinoma.

Vertical transmission from mother to fetus occurs in about 20% of HBsAg-positive pregnant women and about 60% of women who had a primary infection during pregnancy. Since the frequency of vertical transmission of hepatitis infection varies according to geographical area and population, it is suggested that the susceptibility to intrauterine infections depends on the virus strain and the genetic structure of the population. Pregnant women who have been diagnosed with HbsAg require additional testing (determination of replication markers (HbeAg) and identification of the pathogen DNA by PCR).

HBsAg is the most common serological marker for HBV infection (acute and chronic), however, it should be noted that in certain clinical situations, this antigen is not detected in the blood: when the disease develops during the "serological window" of acute hepatitis B (towards HBsAg and its Absence of antibodies); In 10% of cases, co-infection with hepatitis D virus (joint infection) is observed due to the inhibitory effect of hepatitis D virus and in rare cases of mutant forms of hepatitis B virus mutants. Therefore, to confirm a negative HBsAg test result, it is optimal to detect antibodies to HBcorAg.

When should we test for hepatitis B surface antigen (HBsAg)?

• Increase in ALT and AST levels;
• Clinical signs of acute or chronic viral hepatitis, chronic diseases of the liver and bile ducts;
• Examination of the disease in the family / team;
• Preparation for vaccination;
• Examination of patients undergoing frequent parenteral manipulations;
• Preparation for hospitalization, surgery;
• Pregnant women and preparations for pregnancy;
• Preventive screening of donors, people at risk (health workers, children of mothers carrying HBsAg);
• Unprotected sex, frequent change of sexual partners;
• Intravenous drug users.

How to prepare for the test?

No special training is required. The test is preferably fasted.

Research material

Venous blood

Possible interpretation of the results

Positive result:

• Acute hepatitis B (anti-Hbs antibodies are not detected in blood serum during the incubation or acute period);
• Fulminant course of hepatitis B (presence of anti-HBs antibodies and HBsAg in blood serum);
• Chronic hepatitis B;
• HBsAg carriage;
• False Positive Reaction - Confirmation Needed - Re-testing and determination of common HBcorAg antibodies.

Negative result:

• Absence of HBV infection (in the absence of other markers of hepatitis B);
• Acute hepatitis B is not excluded;
• Chronic hepatitis B with low intensity of replication is not excluded;
• Fulminant course of hepatitis B;
• Hepatitis B with defective (seronegative) HBsAg is not excluded;
• Mixed hepatitis B + D (Delta virus uses the surface antigen as its membrane, so the antigen may not be detected).

Resources

https://www.synevo.bg/hepatit-b-hbsag/
https://spravochnik.synevo.ua/ru/gepatit/virus-gepatita-b.html