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HBsAg

Hepatitis Biomarker

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Collection Type: Blood

Body System

Related System: Hepatitis

Overview

Hepatitis B surface antigen (HBsAg) is a protein on the outer shell of the hepatitis B virus (HBV). The HBsAg blood test detects this antigen and therefore indicates active HBV infection (either acute or chronic). It is used for screening (blood donation, prenatal care), diagnosing unexplained jaundice or hepatitis symptoms (fatigue, abdominal pain, dark urine, pale stools, fever), and monitoring patients with known HBV. Results vary by age and exposure route: infants infected at birth are far more likely to develop chronic infection than adults, and immunosuppressed patients may show atypical patterns or reactivation.

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Test Preparation

No special preparation is required

Why Do I Need This Test

Profile: Hepatitis (HBV) screening/diagnostic panel.
Symptoms indicating test: jaundice, persistent fatigue, abdominal pain, dark urine, unexplained elevated liver enzymes.
Diagnoses/monitoring: detects acute HBV, establishes chronic infection, screens blood donors and pregnant women, monitors known HBV carriers.
Reasons for abnormal (positive): current HBV infection, recent exposure, or rarely false-positive assay.
Biological meaning: positive = circulating viral surface antigen → active viral replication or presence.
Behaviors/lifestyle: unprotected sex, IV drug use, occupational exposures, travel to endemic areas.
Family history: mother or household contact with HBV, known chronic carriers.

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Understanding Test Results

A negative HBsAg means no detectable surface antigen, suggesting no active HBV infection (but a very early “window” period may give a false-negative).
A positive HBsAg indicates active hepatitis B infection.
If HBsAg is present for less than about 6 months it generally reflects acute or recent infection; persistence of HBsAg beyond 6 months defines chronic HBV infection and increased risk of liver inflammation, cirrhosis, and hepatocellular carcinoma.
Concurrent tests guide interpretation: anti‑HBc IgM with HBsAg suggests acute infection; HBeAg or high HBV DNA indicates high infectivity/viral replication.
Low or equivocal positives can be transient or false positives repeat testing and HBV DNA confirmation are recommended.

Normal Range

Negative Not detected (qualitative no numeric units)

FAQs

Q: What is Hep B surface antigen HBsAg positive?

A: HBsAg positive means hepatitis B surface antigen is detectable in the blood, indicating current hepatitis B infection (acute or chronic) and potential infectivity. It prompts further testing (anti‑HBs, anti‑HBc IgM/IgG, HBV DNA, liver function) to determine stage and need for treatment. Chronic positivity (>6 months) requires monitoring and possible antiviral therapy; close contacts should be screened and vaccinated if susceptible.

Q: How serious is HBsAg positive?

A: HBsAg positive means you have an active hepatitis B infection (acute or chronic). Many people are asymptomatic, but chronic infection can lead over years to cirrhosis, liver failure, or hepatocellular carcinoma in a minority. Further testing (HBV DNA, liver enzymes, HBeAg) and regular monitoring determine severity; antiviral treatment is available when indicated. Inform and vaccinate close contacts and see a clinician promptly.

Q: How to treat hepatitis B in pregnancy?

A: Pregnant women should be screened for hepatitis B early and, if positive, have viral load assessed. For high HBV DNA (commonly >200,000 IU/mL) start tenofovir in the third trimester to reduce mother-to-child transmission. Newborns should receive hepatitis B vaccine plus hepatitis B immunoglobulin within 12 hours of birth. Monitor maternal liver function during pregnancy and postpartum; breastfeeding is allowed after neonatal immunoprophylaxis.

Q: What is the HBsAg normal range?

A: The normal result for HBsAg (hepatitis B surface antigen) is negative—reported as “not detected” or “non‑reactive.” A positive/reactive HBsAg indicates current hepatitis B infection. Quantitative cutoffs vary by laboratory and assay, commonly around 0.05–0.1 IU/mL; values below the assay cutoff are considered negative. If HBsAg is positive, clinical follow‑up and further testing are recommended.

Q: How long does HBsAg stay positive in the body?

A: HBsAg typically appears 1–10 weeks after exposure. In acute hepatitis B it usually clears within 4–6 months; persistence beyond six months indicates chronic infection. In chronic cases HBsAg can remain detectable for years or lifelong, though some people clear it spontaneously or after antiviral therapy. Regular testing and medical follow-up determines status and guides treatment.

Q: Can HBsAg positive turn negative?

A: Yes. In acute hepatitis B, most healthy adults clear HBsAg within months and become HBsAg-negative. In chronic infection (HBsAg >6 months), spontaneous HBsAg loss is uncommon but can occur over years; antiviral or interferon therapy may increase the chance. HBsAg loss indicates better prognosis, but regular monitoring and specialist-directed care are essential.