HBsAg

HBsAg is the basic blood test for hepatitis B virus infection. A confirmed positive result most often indicates infection, recent or longstanding. A temporarily positive result without infection can also follow recent vaccination. Testing can provide an answer after risky contact, in pregnancy or with raised liver results.

Who the test is for

• you had risky contact: a needlestick, unprotected sex or shared drug-injection equipment;
• a partner or household member has hepatitis B;
• you are pregnant: testing is part of usual pregnancy investigations because the virus can pass to the baby during birth;
• you have raised liver enzymes, jaundice, dark urine or prolonged fatigue;
• you are preparing for chemotherapy, biological medicines, other immune-suppressing treatment or dialysis;
• you are unvaccinated against hepatitis B and want to check your status.

What the test reveals

HBsAg is surface antigen, part of the hepatitis B viral envelope. It appears in blood one to ten weeks after infection, often before symptoms. Infection is chronic if it remains positive for more than six months.

HBsAg indicates infection but not protection. Protection through vaccination or past infection is shown by anti-HBs, while previous infection is shown by anti-HBc. We explain how markers are interpreted together in the article Hepatitis A, B and C markers.

The procedure and preparation

A venous blood sample is taken and collection takes a few minutes. Fasting is unnecessary. Mention hepatitis B vaccination within the last month before collection: a temporarily positive result without infection can rarely occur during that period.

What your result means

Results are positive or negative. A doctor interprets them alongside symptoms, liver enzymes, vaccination history and other hepatitis markers.

• Negative: HBsAg was not found in blood. If little time has passed since risky contact, repeat testing is needed. Negative HBsAg does not mean protection.
• Positive: a reactive result needs confirmation and interpretation. Confirmed positive HBsAg most often indicates hepatitis B infection, transmissible to others. A temporarily positive result without infection can follow recent vaccination, so a doctor considers vaccination history. Additional markers such as anti-HBc IgM, HBeAg and HBV DNA PCR help establish whether infection is recent or chronic, with referral to an infectious diseases specialist or gastroenterologist.
• Positive for more than six months: chronic hepatitis B. Regular monitoring protects the liver, and when treatment is needed the disease is successfully controlled with antiviral medicines.

If sleepiness, confusion, bleeding or severe vomiting accompany yellow skin, go to an emergency department or call 194 or 112 immediately.

How to arrange testing

You can have blood taken without an appointment or referral at one of our branches across Croatia (listed under Contact). Prices for all tests and panels are available in the price list. To check hepatitis C as well, the same collection can also provide anti-HCV.

Frequently asked questions

What does positive HBsAg mean?

Confirmed positive HBsAg most often indicates hepatitis B infection. A temporarily positive result without infection can also follow recent vaccination. HBsAg alone does not show whether infection is recent or chronic, so a doctor considers vaccination history and additional tests. Household members and partners should be tested and vaccinated if unprotected.

Does negative HBsAg mean I am protected?

No. Negative HBsAg means only that HBsAg was not currently detected. Anti-HBs indicates protection after vaccination or past infection.

How is hepatitis B transmitted?

Through blood, sexual contact and mother-to-child transmission during birth. It is not transmitted by hugging, kissing or shared cutlery. Vaccination is the best protection.

How soon after risky contact is testing useful?

HBsAg becomes measurable one to ten weeks after infection. Testing can be performed immediately, but a negative result in the first weeks needs repeating. After a needlestick or similar exposure, contact a doctor promptly because vaccination and immunoglobulin protect best when given early, preferably within 24 hours.