Hepatitis B Surface Antigen Test: Purpose, Procedure, and Interpretation

Diagnosis of Hepatitis B has entered a new era with the advent of quantitative Hepatitis B surface antigen test (HBsAg). Unlike traditional qualitative tests, quantitative HBsAg assays measure the actual amount of surface antigen in the blood. It now allows healthcare providers to monitor disease progression more accurately.

Moreover, quantitative HBsAg levels can help distinguish between inactive carriers and those with active disease. As we explore the Hepatitis B surface antigen test, know that it is strengthening our approach to hepatitis B management and improving patient care.

How Hepatitis B is Caused

Hepatitis B is caused through contact with infected blood, semen, or bodily fluids. It is possible if you:

• Share needles for IV drug use.
• Live with a person who has chronic hepatitis B.
• Work in jobs involving exposure to human blood.
• Have unprotected sex with multiple partners or infected individuals.
• Were born to a mother with HBV.
• Travel to areas with high HBV prevalence, like Asia, the Pacific Islands, Africa, or Eastern Europe

Hepatitis B Surface Antigen Test

The Hepatitis B surface antigen test screens for hepatitis B and diagnoses acute or chronic infections. It is also used to monitor those at risk, like individuals with HIV or recent exposure to the virus.

The HBsAg test is the main tool for detecting acute hepatitis B, which occurs within the first six months of HBV exposure. HBsAg appears 2–10 weeks after infection and remains detectable for up to six months. It's commonly done using a blood sample, but can also use saliva, semen, or vaginal fluid.

Why HBsAg test is done?

The Centers for Disease Control and Prevention (CDC) says that anyone experiencing symptoms like abdominal pain, dark urine, loss of appetite, fever, nausea, vomiting, joint pain, fatigue, weakness, or yellowing of the skin and eyes (jaundice) should take HBsAg test.

How to Diagnose Hepatitis B

Hepatitis B is identified through a blood test called the hepatitis B panel. It involves the following three tests.

1. HBsAg: It detects the presence of the hepatitis B virus (HBV) in your blood. A positive result means you have an active infection and can spread the virus. It is also known as the Australia antigen test.
2. Hepatitis B Core Antibody (HBcAb): This test checks if you have ever been exposed to HBV by detecting antibodies made in response to the infection. It can indicate either a current or past infection.
3. Hepatitis B Surface Antibody (HBsAb): This test shows if your immune system has developed antibodies against HBV, either from a past infection or from vaccination, meaning you are protected from future infections.

HBsAg Test Procedure

The Hepatitis B surface antigen test involves drawing a blood sample through venipuncture. A healthcare professional will insert a needle to collect the sample. After enough blood is drawn, the needle is removed. The blood sample is then sent to a lab for analysis.
In some cases, a rapid HBsAg test may be used to test the blood using a diagnostic tool. This test involves applying the blood sample to a device coated with antibodies that react with the HBsAg. It causes a colour change if the antigen is present.
After the test, you may feel slight discomfort or lightheadedness, but it passes quickly. Eating and drinking after the test can help minimize any side effects. Results usually take a few days to be processed.

Interpreting HBsAg Test Results

A positive result in the Hepatitis B surface antigen test indicates an active HBV infection and it can be transmitted to others. Upon receiving a positive result, it's essential to consult a doctor for further testing to determine if the infection is acute (short-term) or chronic (lasting more than six months).

What is the HBsAg Positive

• A positive HBsAg result confirms that HBV is in the bloodstream.
• Acute HBV infections are usually resolved within six months. After that, the individual becomes immune to future infections and cannot spread the virus.
• Chronic HBV infections occur when the virus remains in the blood for over six months, which can lead to serious liver issues, e.g. cirrhosis or liver cancer. Chronic carriers may not be contagious at all times but can still experience reactivation.

Further Testing After a Positive HBsAg

• Your physician may suggest a viral load test or liver enzyme tests (ALT and AST) to assess the severity of the infection and the extent of liver damage.
• These tests help healthcare providers determine the level of virus in the blood and whether the infection is active or inactive.

Negative HBsAg Result

• A negative HBsAg result means that no HBV infection is present.
• If other tests in the hepatitis B panel are negative, it indicates that the person is not immune to HBV and may be at risk of infection. Vaccination is recommended for such individuals.
• If other panel test results are unclear, repeat testing may be suggested.

Factors Influencing the Test Results

Immunosuppression can lead to higher HBsAg levels.

1. Viral Mutations: Some virus variants might evade detection in certain tests.
2. Recent Vaccination can cause temporary false-positive results.
3. Advanced liver disease might affect HBsAg production.
4. Antiviral therapy can reduce HBsAg levels.

Conclusion

While the Hepatitis B surface antigen test has improved our comprehension of HBV, remember that HBV management goes beyond diagnosis. Lifestyle modifications, alcohol avoidance, and a balanced diet are still important for liver health.

Regularly monitor your liver function and hepatocellular carcinoma for long-term care. Lastly, emotional support and patient education support in leading a successful life with hepatitis B.

Also read: Viral Marker Tests: Purpose, Procedure & Costs