Hepatitis B Surface Antigen (HBsAg)
Hepatitis B surface antigen (HBsAg) testing is used to evaluate several aspects related to hepatitis B virus (HBV) infection:
- Diagnosis of Acute or Chronic Hepatitis B Infection: HBsAg testing is the primary diagnostic test for hepatitis B infection. The presence of HBsAg in the blood indicates active HBV infection. HBsAg testing is used to diagnose both acute and chronic hepatitis B. Acute hepatitis B infection is characterized by the presence of HBsAg along with other markers such as hepatitis B core antibody (anti-HBc) IgM. Chronic hepatitis B infection is diagnosed if HBsAg persists in the blood for six months or longer.
- Screening for Hepatitis B Infection: HBsAg testing is used for screening individuals who may be at risk of HBV infection, such as those with a history of high-risk behaviors (e.g., unprotected sex, injection drug use), individuals born in regions with high HBV prevalence, healthcare workers, pregnant women, and individuals with liver disease or abnormal liver function tests.
- Identification of Carriers: HBsAg testing helps identify individuals who are carriers of HBV, meaning they have chronic HBV infection and can potentially transmit the virus to others. HBsAg-positive individuals are considered infectious and may require monitoring for liver disease progression and initiation of antiviral therapy to suppress HBV replication.
- Assessment of Hepatitis B Vaccination Status: HBsAg testing can be used to assess hepatitis B vaccination status. The presence of HBsAg indicates natural HBV infection, while the absence of HBsAg along with the presence of hepatitis B surface antibody (anti-HBs) indicates immunity due to vaccination.
- Monitoring Disease Progression: In individuals with chronic hepatitis B, HBsAg testing may be performed periodically to monitor disease activity and assess response to treatment. Decline or loss of HBsAg during treatment (seroconversion) may indicate a favorable treatment response and reduced risk of liver complications.
- Prevention of Mother-to-Child Transmission: HBsAg testing is used in prenatal care to screen pregnant women for HBV infection. Positive HBsAg status in pregnant women prompts additional interventions, such as administration of hepatitis B immune globulin (HBIG) and hepatitis B vaccine to newborns, to prevent mother-to-child transmission of HBV.