What does a positive Hepatitis B Surface Antigen (HBsAg) result mean?

Interpretation of Positive Hepatitis B Surface Antigen (HBsAg) Test

A positive Hepatitis B Surface Antigen (HBsAg) test definitively indicates current HBV infection, which may be either acute or chronic, and confirms that the person is infectious. 1

Clinical Significance of Positive HBsAg

• HBsAg is the hallmark of HBV infection and is the first serological marker to appear in acute hepatitis B 1
• All HBsAg-positive individuals should be considered infectious and capable of transmitting the virus to others 1
• In newly infected persons, HBsAg is typically detectable 30 days after exposure (range: 6-60 days) 1
• HBsAg appears in serum 4 weeks before clinical symptoms develop in acute infection 1

Distinguishing Acute vs. Chronic Infection

• If HBsAg persists for more than 6 months, the infection is classified as chronic, and spontaneous clearance becomes unlikely 1
• Additional testing for IgM anti-HBc helps distinguish between acute and chronic infection:
  • Positive IgM anti-HBc indicates acute or recent infection 1
  • Negative IgM anti-HBc with positive HBsAg suggests chronic infection 1
• Chronic infection occurs in approximately:
  • 90% of infected infants
  • 30% of infected children under 5 years
  • Less than 5% of infected persons over 5 years of age 1

Complete Serologic Profile Interpretation

The following patterns help determine the exact stage of HBV infection:

HBsAg	Total anti-HBc	IgM anti-HBc	Anti-HBs	HBV DNA	Interpretation
+	-	-	-	+ or -	Early acute infection [1]
+	+	+	-	+	Acute infection [1]
+	+	-	-	+	Chronic infection [1]

Clinical Implications and Management

• All patients with positive HBsAg require medical evaluation and regular monitoring 1
• Persons with chronic HBV infection are at risk for:
  • Liver cirrhosis
  • Hepatic decompensation
  • Hepatocellular carcinoma (HCC) 2
• Approximately 25% of those with chronic infection acquired in childhood die prematurely from cirrhosis or liver cancer 1
• Therapeutic agents can achieve sustained suppression of HBV replication and remission of liver disease in certain persons 1
• Pregnant women who are HBsAg-positive require special management to prevent perinatal transmission 1

Common Pitfalls in Interpretation

• Transient HBsAg positivity can occur for up to 18 days following hepatitis B vaccination, which is clinically insignificant 1
• False-positive results can occur, so confirmatory testing is recommended for asymptomatic individuals with unexpected positive results 1
• HBsAg variants may affect the sensitivity of diagnostic assays, potentially leading to false-negative results 3
• Occult HBV infection can occur when HBsAg is undetectable despite the presence of HBV DNA 1

Next Steps After Positive HBsAg

1. Complete serologic profile including:

   • HBsAg (already positive)
   • Total anti-HBc and IgM anti-HBc (to determine acute vs. chronic)
   • Anti-HBs (to assess immunity)
   • HBV DNA (to assess viral replication) 1

2. Evaluate liver function with liver enzyme tests 1

3. Consider screening for hepatocellular carcinoma in those with chronic infection 1

4. Implement measures to prevent transmission to close contacts 1

5. Refer patients with chronic HBV infection to specialists experienced in managing such infections 4