Finding the right tests…
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Finding the right tests…
Serology
HBsAg is a protein found on the outer coat of the hepatitis B virus, and this test looks for it directly in your blood. Its presence means the virus is currently active in your body - either as a new, acute infection or as a long-term, chronic one - rather than a past infection that has already cleared. Doctors order it when investigating unexplained jaundice, fatigue, or abnormal liver enzymes, and as part of routine antenatal screening, since hepatitis B can pass from mother to baby during delivery. After a known exposure, HBsAg can usually be detected within about one to nine weeks, averaging around one month.
A positive HBsAg result confirms the virus is present and active, but it alone does not distinguish a brand-new infection from one a person has carried for years. Telling the two apart needs an additional antibody test - IgM antibody to the hepatitis B core antigen - which is positive only in a recent infection. A negative HBsAg result does not completely rule out infection either, particularly very early after exposure or during recovery, which is why doctors often order it as part of a fuller hepatitis B panel rather than alone.
A positive HBsAg result means hepatitis B virus is currently present in your blood. On its own, that does not say whether the infection is new or long-standing - both look the same on this one test. Your doctor adds a core antibody test to tell the two apart, since a new infection is managed differently from a chronic one that may need long-term monitoring.
Most adults who catch hepatitis B for the first time clear the virus within a few months, and their HBsAg eventually turns negative on its own. A smaller number, more often those infected in infancy or early childhood, do not clear it and stay HBsAg-positive for years - a chronic infection that raises the long-term risk of liver scarring and liver cancer, and needs regular monitoring even without symptoms.
- A mother who is HBsAg-positive can pass the virus to her baby during delivery - Testing in pregnancy allows the baby to get hepatitis B vaccine and immune globulin at birth, which is highly effective at preventing transmission - This is one of the reasons HBsAg testing is routine in antenatal panels, not just for people with symptoms
A single positive result is the start of a workup, not the end of one - your doctor uses further blood tests to decide whether the infection is acute or chronic, and what monitoring or treatment you need.
A positive result means hepatitis B virus is currently active in your blood, either as a new or a long-standing infection. Your doctor orders additional antibody tests to tell which one it is and to plan monitoring or treatment.
HBsAg can usually be detected as early as about one week and as late as nine weeks after exposure, averaging around one month. Testing too soon after a specific exposure can still miss an early infection.
No, HBsAg alone looks the same in both cases. Your doctor adds an IgM core antibody test, which is positive only in a recent infection, to tell a new infection apart from a chronic one.
This page is general information about the test, not medical advice. Your own report's reference ranges apply — please discuss your results with your doctor.
A mother who is HBsAg-positive can pass hepatitis B to her baby during delivery. Knowing this in advance lets the baby receive hepatitis B vaccine and immune globulin at birth, which is highly effective at preventing transmission.
There is no fasting requirement for this test. Ask your doctor or the centre when you book if other blood work is planned at the same time.
Yes, HBsAg can show a brief, false positive for about a month after a dose of hepatitis B vaccine. Doctors take a recent vaccination date into account when reading a positive result close to that timeframe.