Hepatitis B Surface Antigen (HBsAg) (Quantitative)
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It indicates high levels of viral replication and infectivity in individuals with chronic or acute hepatitis B
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🧪 What is HBsAg (Quantitative)?
HBsAg (Hepatitis B surface antigen) is a protein present on the surface of the Hepatitis B virus (HBV).
The quantitative HBsAg test measures the concentration of HBsAg in the blood and helps monitor disease activity and treatment response in HBV infection.
- It differs from the qualitative HBsAg test, which only tells you positive or negative.
- It is reported in IU/mL (International Units per milliliter).
❓ Why is the Test Done?
To:
- Diagnose and monitor chronic Hepatitis B infection
- Assess viral replication indirectly when HBV DNA is not available
- Evaluate treatment response (e.g., peg-interferon or antiviral therapy)
- Monitor disease progression and assess risk of liver damage
- Help in HBV reactivation risk assessment (e.g., before chemotherapy)
📊 Normal Range / Reference Values
Result (IU/mL) | Interpretation |
|---|---|
< 0.05 IU/mL | Negative – No active HBV infection |
≥ 0.05 IU/mL | Positive – Indicates HBV infection |
High levels (>1,000 IU/mL) | Suggest active replication (especially with high HBV DNA) |
Declining levels | Suggest treatment response or spontaneous clearance |
Thresholds may vary by lab methodology.
📈 Interpretation of Quantitative HBsAg Levels
HBsAg Level | Clinical Implication |
|---|---|
<0.05 IU/mL | No surface antigen detected → likely recovered or vaccinated |
<100 IU/mL | Low replication / inactive carrier state (especially if HBV DNA is also low) |
>1,000 IU/mL | High viral replication and/or treatment non-response |
Decline >1 log over time | Suggests response to interferon therapy |
HBsAg clearance | Indicates viral resolution or long-term remission (rare in chronic HBV) |
🧠 Associated Organs & Conditions
Organ | Conditions |
|---|---|
Liver | - Acute and Chronic Hepatitis B |
Immune System | Inability to clear HBsAg leads to chronic carrier state |
🔄 Related / Follow-Up Tests
- HBV DNA (Quantitative PCR) – Direct measure of viral load
- HBeAg & Anti-HBe – Replication and seroconversion markers
- Anti-HBs – Immunity marker post-recovery or vaccination
- Liver Function Tests (ALT, AST, Bilirubin) – Assess liver damage
- Liver Fibrosis/Elastography (FibroScan)
- Alpha-fetoprotein (AFP) – HCC screening in chronic carriers
✅ Fasting Required?
Test | Fasting Required |
|---|---|
HBsAg (Quantitative) | ❌ No fasting required – Blood sample can be taken anytime |
📝 Summary Table
Parameter | Description |
|---|---|
What | Measures the amount of Hepatitis B surface antigen in the blood (IU/mL) |
Why | Assess HBV activity, infectivity, monitor treatment, and guide prognosis |
Normal | <0.05 IU/mL (negative) |
High Result | Suggests active HBV infection and high replication |
Follow-up Tests | HBV DNA, HBeAg, Anti-HBs, LFTs, AFP, imaging |
Associated Conditions | Acute/chronic HBV, cirrhosis, liver cancer |
Fasting Required | ❌ No |
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