Hepatitis B “s” Ag (HBs Ag) Test – Screen for Hepatitis B Infection

The Hepatitis B Surface Antigen (HBs Ag) Test detects the presence of the hepatitis B surface antigen in the blood, indicating an active hepatitis B virus (HBV) infection. This test is a cornerstone of viral hepatitis screening and is used to diagnose acute or chronic HBV, monitor infection status, and determine immunity or carrier state.

Symptoms That Indicate You May Need This Test

If you experience any of the following, especially with risk factors like IV drug use, unprotected sex, or travel to endemic areas:

 
• Fatigue and weakness
 
• Jaundice (yellowing of skin and eyes)
 
• Dark urine and pale stools
 
• Abdominal pain, especially in the upper right quadrant
 
• Nausea, vomiting, or loss of appetite
 
• Joint pain and fever
 

These may indicate acute hepatitis B infection. However, many people are asymptomatic, making screening essential.

Natural Production and Role in the Body

The hepatitis B surface antigen (HBsAg) is a protein found on the surface of the hepatitis B virus. It appears in the blood 6–16 weeks after exposure and is the first marker of infection. Its presence indicates that the virus is actively replicating and the person is contagious. In acute infection, HBsAg usually disappears within 6 months. Persistence beyond 6 months suggests chronic infection.

What Happens If Left Untreated?

Chronic hepatitis B can lead to severe liver complications, including:

 
• Cirrhosis (scarring of the liver)
 
• Liver failure
 
• Hepatocellular carcinoma (liver cancer)
 
• Transmission to others through blood or bodily fluids
 
• Fulminant hepatitis (rare but life-threatening)
 

Early detection allows for monitoring, antiviral treatment, and lifestyle changes to protect liver health.

Test Overview

A 2 mL blood sample is collected in an SST or red-top tube. The test uses immunoassay methods to detect HBsAg in serum. Results are typically available the same day. A positive result requires follow-up testing (e.g., HBV DNA, liver function tests) to determine infection stage and treatment needs.

Frequently Asked Questions (FAQs)

Can I have hepatitis B without symptoms?

Yes—many people, especially children, have no symptoms but can still spread the virus.

Does a positive test mean I’m immune?

No—positive HBsAg means active infection. Immunity is indicated by positive anti-HBs antibodies, usually from vaccination or recovery.

Who should get tested?

Recommended for pregnant women, healthcare workers, people with multiple sexual partners, IV drug users, and those from regions with high HBV prevalence.