Definition

HBsAg (Hepatitis B Surface Antigen) is a protein located on the outer surface of the hepatitis B virus. Its presence increases when the body is infected with hepatitis B, whether in its acute or chronic form.

HBsAg can be detected in the blood anywhere from 1 to 10 weeks after exposure to the hepatitis B virus. If the infection is resolved, this protein typically disappears within 4 to 6 months. However, if HBsAg remains in the blood for more than 6 months, it is likely that the person has chronic hepatitis B infection.

HBsAg encases HBcAg (hepatitis B core antigen), a protein that protects the virus’s DNA from replication. HBcAg helps shield the virus from attacks by the body’s immune system. Despite this, the immune system can still target and attack the virus.

Dead hepatitis B viruses can leave behind residual antigen proteins from the surface of the virus and remain in the bloodstream, so they can be detected in blood tests.

HBsAg tests are used to detect the presence of hepatitis B infection. Elevated levels of HBsAg indicate an active infection with the hepatitis B virus.

Typically, the HBsAg test is conducted alongside other blood tests, such as anti-HBs (hepatitis B surface antibody), anti-HBc (total antibody to hepatitis B core antigen), and IgM anti-HBc (IgM antibody to hepatitis B core antigen). 

Indication

Your doctor may recommend this test if there is a suspicion that you have been infected with hepatitis B. Symptoms of hepatitis B can range from mild to severe and typically appear 1 to 4 months after exposure to the virus. Common symptoms include:

• Abdominal pain

• Dark urine

• Fever

• Joint pain

• Loss of appetite, nausea, and vomiting

• Fatigue and tiredness

• Jaundice (yellowish tint to the skin and the whites of the eyes)

The HBsAg test is also recommended for individuals who are at high risk of contracting hepatitis B, such as:

• Pregnant women

• Individuals who have not been vaccinated against hepatitis B

• Those who are HIV positive

• People who use injectable drugs

• Individuals with multiple sexual partners

Contraindication

There are no specific contraindications that would prevent someone from taking the HBsAg test. This test is generally safe for people of all ages.

Preparation Before the Test

The HBsAg test does not require any special preparation, and fasting is not necessary. However, it is advisable to consult with a doctor before undergoing the test to ensure that any conditions that might affect the accuracy of the results are addressed.

Test Procedure

The HBsAg test typically requires a blood serum sample of 0.25 to 0.5 ml, which is collected from a vein. This sample is placed in a special tube. Laboratory personnel will wear gloves and other personal protective equipment (PPE) when collecting the sample.

Before drawing the blood, the healthcare professional will apply an elastic band to your arm and clean the puncture site with antiseptic gauze. Blood is typically drawn from the area inside your elbow. After the blood is drawn and placed into the tube, the elastic band will be removed, and the puncture site will be cleaned with antiseptic gauze. This process usually takes only a few minutes. The blood sample is then analyzed in the laboratory, and results are typically available within a few hours.

Normal and Abnormal Values

Normal HBsAg values are generally not differentiated based on age or gender. The following are the normal and abnormal values for HBsAg test results:

Results and Recommendations (Follow-up Tests)

Negative Results

A negative result on the HBsAg test means you are not currently infected with hepatitis B. To maintain good health, it is recommended to eat a balanced diet, stay active, and undergo regular health check-ups.

Negative results may also occur in individuals who have recovered from a hepatitis B infection on their own. If you have received the hepatitis B vaccine, the test will likely return a negative result as well.

Positive Results

If the HBsAg test result is positive, it is important to consult a doctor. A positive result indicates that the body is actively infected with the hepatitis B virus. In this case, you could transmit the virus to others through blood or other body fluids.

A positive HBsAg result could also indicate acute or chronic hepatitis B infection or suggest a past infection with hepatitis B.

If you recently received a hepatitis B vaccination, the test might also show a positive result. In this case, the doctor will recommend waiting for at least one month after the vaccination before taking the test to ensure accurate results.

The doctor will also suggest further tests and review results from other tests (such as anti-HBs, anti-HBc, and IgM anti-HBc) to determine whether the hepatitis B infection is acute or chronic.

Consult the Right Doctor

If your HBsAg test results are positive, it is crucial to immediately consult a general practitioner or an internist. A positive result means that your body is infected with the hepatitis B virus, and you will need further treatment and care to prevent complications associated with hepatitis B.

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