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Serum or plasma concentration of hepatitis B surface antigen (HBsAg) by immunoassay

Published: August 9, 2026Updated: August 16, 2026

This test checks for the presence of hepatitis B surface antigen in your blood, which indicates whether you have an active hepatitis B virus infection or have been exposed to it recently.

Quick summary

["HBsAg helps determine if you need further testing or treatment for hepatitis B."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 16, 2026Editorial policy

Key facts at a glance

LOINC
63682-9
Short code
Drug continue cause hepatitis SSAGA II
Synonyms
Drug continue cause hepatitis SSAGA II
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
ssaga-ii
Specimen volume
5 mL
Stability
Room temperature: 4h, Refrigerated: 24h, Frozen: 7d
Hemolysis max
500
Lipemia max
1000
Icterus max
500
TAT
4–24 hours
Order
routine

What This Test Measures

The hepatitis B surface antigen (HBsAg) is a protein produced by the hepatitis B virus. If it appears in your blood, it means the virus is actively replicating, which can lead to liver damage if untreated. This test detects the presence of HBsAg using an immunoassay method, which identifies antibodies or antigens in your blood sample.

Why It’s Done

Doctors order this test to diagnose hepatitis B infection, assess the risk of transmission to others, or monitor the progression of the disease. It may also be used during pregnancy to check for infection in the mother and potential transmission to the baby.

Sample Collection and Preparation

A blood sample is taken from a vein in your arm. The blood is then processed to separate the serum or plasma, which is tested for HBsAg. This test can be performed on serum or plasma, depending on the lab’s standard procedure.

Interpreting Results

A positive result means HBsAg is present, suggesting an active infection. A negative result indicates no detectable antigen at the time of testing. Follow-up testing may be needed to confirm infection or monitor treatment effectiveness.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance

Short name

Hepatitis B Surface Antigen (HBsAg) Test

Frequently asked questions

Why might my doctor want to know if I have hepatitis B?
Your doctor may order this test if you have symptoms like fatigue, jaundice (yellowing of the skin or eyes), abdominal pain, or unexplained liver issues. It’s also recommended for people at higher risk of hepatitis B, such as those with multiple sexual partners, intravenous drug users, or those born to infected mothers. Early detection allows for prompt treatment and reduces the risk of long-term liver damage.
What does a positive result mean for my health?
A positive HBsAg test means you currently have an active hepatitis B infection. This requires medical evaluation to determine the stage of infection and whether treatment is needed. Your doctor may recommend monitoring liver function, vaccinations for others, and possibly antiviral therapy to manage the infection and prevent complications like chronic liver disease or cirrhosis.
Can I still transmit hepatitis B if my test is positive?
Yes, if your HBsAg test is positive, you can transmit the hepatitis B virus to others through blood, semen, vaginal fluids, or other bodily fluids. This includes during sex, sharing needles, or from mother to baby during childbirth. Protective measures like avoiding sharing personal items, using condoms, and avoiding risky behaviors can help prevent transmission.
  1. 1
    MedlinePlus — Laboratory TestsSource
  2. 2
    Lab Tests OnlineSource
  3. 3
    Mayo Clinic — Tests & ProceduresSource

Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.

This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.

Medical Disclaimer

This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.

If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.

Medically reviewed by WellAlly Editorial Team Last reviewed August 16, 2026. · Read our editorial policy