Hepatitis B virus, surface antigen (HbsAg)
Why this test?
- To control chronic hepatitis B (prescribed together with the determination of other antigens and antibodies to the hepatitis B virus).
- To determine transferred viral hepatitis B and the development of post-infectious immunity.
- To assess the effectiveness of vaccination and the development of post-vaccination immunity.
- For the selection of people with risk factors for HBV infection for the purpose of vaccination.
- To decide on the expediency of prescribing immunoglobulin to patients with viral hepatitis and a high risk of infection.
In what cases is it prescribed?
- Every 3-6 months during control of chronic viral hepatitis B and its treatment.
- If there is data on transferred hepatitis of unknown etiology.
- When examining patients from the group of high risk of contracting HBV.
- When deciding on the need for vaccination against viral hepatitis B.
- Several months or years after the vaccine is administered.
Viral hepatitis B (HBV) is an infectious liver disease caused by the DNA-containing hepatitis B virus (HBV). Among all the causes of the development of acute hepatitis and chronic viral infection, the hepatitis B virus is considered one of the most common in the world.
The true number of infected people is unknown, because many people have the infection without obvious clinical symptoms and do not seek medical help. The virus is often detected during preventive laboratory tests. According to approximate estimates, about 350 million people in the world are affected by the hepatitis B virus, and 620,000 die annually from its consequences.
The source of infection is a person suffering from HBV or a virus carrier. HBV is transmitted through blood and other body fluids. It is possible to become infected through unprotected sexual contact, when using non-sterile syringes, during blood transfusions and transplantation of donor organs, in addition, the infection can pass from mother to child during or after childbirth (for example, through cracks in the nipples).
The risk group includes medical workers who may come in contact with the patient's blood, patients on hemodialysis, injection drug users, people with numerous unprotected sexual relations, children born to mothers with HBV. The incubation period of the disease is from 4 weeks to 6 months. Viral hepatitis B can occur both in the form of mild forms that last for several weeks, and in the form of a chronic infection with a long course.
The main symptoms of hepatitis: yellowness of the skin, fever, nausea, rapid fatigue, in tests - signs of impaired liver function and specific antigens of the hepatitis B virus. An acute disease can progress quickly, with a fatal outcome, turn into a chronic infection or end with a full recovery. It is believed that persistent immunity is formed after HBV exposure. Chronic viral hepatitis B is associated with the development of cirrhosis and liver cancer.
There are several tests for the diagnosis of current or transferred viral hepatitis B. The determination of viral antigens and antibodies is performed to detect carriage, acute or chronic infection in the presence or absence of symptoms, in the monitoring of chronic infection. The virus has a complex structure. The main antigen of the shell is HBsAg - the surface antigen of the virus. There are biochemical and physicochemical features of HBsAg that allow it to be divided into several subtypes.
Specific antibodies are produced for each subtype. Different antigen subtypes are found in different regions of the world. Anti-HBs antibodies begin to appear in the blood on the 4th-12th week after infection, but immediately bind to HBsAg, so they can be detected in the specified amount only after the disappearance of HBsAg. The period between the disappearance of the antigen and the appearance of antibodies («window» period, or «serological gap») can be from 1 week to several months. Antibody titers grow slowly, reaching a maximum after 6-12 months, and remain high for more than 5 years. Some convalescents have antibodies in their blood for many years (sometimes for life).
Anti-HBs are also formed when antigenic material of the virus is encountered during vaccination against HBV and indicate an effective immune response to the vaccine. But post-vaccination antibodies do not last as long in the blood as post-infection antibodies. Determination of Anti-HBs is used to solve the question of the feasibility of vaccination. For example, with a positive analysis, the introduction of the vaccine is not required, because specific immunity already exists.