Anti-HBs

Anti-HBs are antibodies against hepatitis B surface antigen (HBsAg). The test shows whether you are protected against hepatitis B after vaccination or recovery from infection. It is most often used to check whether protection was achieved after vaccination.

Who the test is for

• healthcare workers and healthcare students after vaccination, when confirming protection is important;
• people on dialysis and immunocompromised people after vaccination;
• sexual partners and household members of people with hepatitis B, and children of mothers with hepatitis B, after vaccination;
• people whose employer or educational institution requires proof of protection;
• adults who do not know whether they were vaccinated or had hepatitis B, before vaccination;
• people with suspected hepatitis B or recovering from infection, alongside other markers.

What anti-HBs is and what it indicates

Hepatitis B is viral liver inflammation transmitted through blood, sexual contact and from mother to child during birth. Some infected people develop chronic infection that can damage the liver over the years.

The body produces anti-HBs after vaccination or recovery from infection. The antibody concentration is called a titre and is expressed in IU/L (equivalent to mIU/mL). A titre of 10 IU/L or above is considered protective.

Anti-HBs alone does not show whether protection came from vaccination or infection, or whether active infection is present. Other hepatitis B markers are measured alongside it for this: HBsAg, which shows the presence of the virus, and anti-HBc, which indicates previous infection. An overview of all markers is available in the article on hepatitis A, B and C markers.

After vaccination, anti-HBs is checked one to two months after the last vaccine dose. In Croatia, children have been routinely vaccinated against hepatitis B since 1999, and infants since 2007, so a large proportion of younger adults are vaccinated.

Preparation and sample

Blood is taken from a vein and fasting is not required. If you recently received hepatitis B immunoglobulin, another immunoglobulin preparation or a blood transfusion, mention it at sampling because antibodies in these preparations may temporarily produce positive anti-HBs.

How results are interpreted

The protective threshold of 10 IU/L is widely accepted, while reporting format depends on the method. A doctor interprets the titre and its meaning alongside vaccination history and other markers. In general:

• 10 IU/L or above: the person is protected against hepatitis B.
• Below 10 IU/L after recent vaccination: protection was not achieved. A doctor usually recommends another vaccination series and repeat titre testing, and HBsAg testing for those who still do not produce antibodies.
• Below 10 IU/L years after vaccination: titres naturally fall over time. If initially protective after vaccination, immune memory generally continues to protect healthy people.

Alongside other markers, results are most often interpreted as follows:

HBsAg	Anti-HBc	Anti-HBs	Most common meaning
negative	negative	positive	protection through vaccination
negative	positive	positive	past infection and naturally acquired protection
negative	negative	negative	no protection or evidence of infection; vaccination recommended
positive	positive	negative	acute or chronic infection; distinguished by anti-HBc IgM and further investigation
negative	positive	negative	several possibilities, from past infection to a false positive; assessed by a doctor

How to arrange testing

You can have blood taken without an appointment or referral at one of our branches across Croatia (listed on the Contact page). Prices for all tests and panels, including HBsAg and anti-HBc, are available in the service price list.

Frequently asked questions

What does positive anti-HBs mean?

Positive anti-HBs, meaning a titre of 10 IU/L or above, means you are protected against hepatitis B. If anti-HBc is negative, protection came from vaccination; if positive, you recovered from infection. Positive anti-HBs generally does not mean you have hepatitis B or are infectious.

What anti-HBs titre is protective?

A titre of 10 IU/L or above measured one to two months after vaccination is considered protective. If protective then, protection in a healthy person lasts even when titres fall below that threshold over time.

Do I need a booster if my titre falls below 10 IU/L?

Boosters are generally not recommended for healthy people who had a protective titre after vaccination. If your initial vaccine response is unknown, particularly important for healthcare workers, a doctor may recommend one vaccine dose and repeat titre testing after one to two months.

Is anti-HBs the same as HBsAg?

No. HBsAg is part of the virus itself and is positive in an infected person, while anti-HBs are protective antibodies. Positive HBsAg means infection, while positive anti-HBs means protection.