Discovering a “positive HBs antigen” result on a blood test can raise questions. This medical term, though technical, is an essential indicator related to the hepatitis B virus. Understanding its meaning is the first step to addressing the situation in an informed way. This article aims to provide clear and factual information to decode this marker, its role, and the implications of a positive result.

What is HBs antigen?

HBs antigen (HBsAg), or hepatitis B surface antigen, is a protein found on the surface of the hepatitis B virus (HBV). It acts as an identification card for the virus, allowing it to be detected in the body. Under normal circumstances, an uninfected person does not have this antigen in their blood.

When the hepatitis B virus multiplies in liver cells, it produces and releases this antigen in large quantities. Therefore, the presence of HBs antigen in the bloodstream is the most direct sign of an active HBV infection. Healthcare professionals rely on its detection to make a reliable diagnosis of hepatitis B.

From a physiological perspective, this antigen provides no benefit to the body. Its mere presence signals that the virus has entered the body and is replicating there. The immune system recognizes it as a foreign element and triggers a response to try to eliminate it. This immune reaction is also the cause of the symptoms that can occur during hepatitis.

Why is it important to understand?

The presence of HBs antigen has implications that go beyond a simple laboratory result. A liver inflamed or damaged by hepatitis B can have its functions altered. This can notably affect protein production, blood clotting, and drug metabolism.

Understanding this antigen has evolved since its discovery in 1965 by Dr. Baruch Blumberg, an advance rewarded with a Nobel Prize. This discovery paved the way for the development of accurate screening tests and effective vaccines, transforming hepatitis B into a better-controlled disease.

Early detection is essential. Indeed, an unmonitored chronic infection can progress to serious complications such as cirrhosis or liver cancer. Appropriate management significantly reduces these risks. HBs antigen screening is therefore crucial for public health, particularly for blood donation safety or during pregnancy monitoring to prevent mother-to-child transmission.

How to read and interpret your test results?

When you receive your results, the line concerning this marker is often presented qualitatively and not quantitatively.

Understanding the Presentation of Results

The result is generally binary:

• HBs Antigen: Positive (or Detected)
• HBs Antigen: Negative (or Not Detected)
• Reference Value: Negative

Laboratories often highlight a positive result with a color (red) or a symbol (asterisk) to draw attention. Unlike markers like cholesterol, there is no range of values. The detection of the antigen, even in small quantities, is sufficient to make the test positive. The methods used today are extremely sensitive and allow for early screening of the infection.

Tips for Effective Interpretation

Here is a list to help you analyze your results:

• Main result: First, check if the result is positive or negative.
• Complementary markers: Look for other hepatitis B markers that are often analyzed at the same time (anti-HBs antibodies, anti-HBc antibodies, HBe antigen). They help to specify the stage of the infection.
• Collection date: The date is important to place the result in time.
• Previous results: If you have any, compare them to see any evolution.
• Medical consultation: A positive result must always be followed by a medical consultation for a complete interpretation and adapted management.

HBs Antigen and Associated Pathologies

A positive HBs antigen result can correspond to several distinct clinical situations.

Acute Hepatitis B Virus Infection

Acute infection is the first phase of the disease, occurring after contamination. HBs antigen becomes detectable in the blood even before the appearance of the first symptoms. In the majority of adults (approximately 95%), the immune system manages to eliminate the virus. HBs antigen then disappears in less than six months. Symptoms, when present, can include fatigue, nausea, or jaundice.

Chronic Hepatitis B

If HBs antigen remains detectable in the blood for more than six months, the infection is considered chronic. This affects approximately 5% of infected adults, but this rate is much higher in infants. Chronicity results from an insufficient immune response to eliminate the virus. Chronic hepatitis B is often asymptomatic for years, hence the importance of screening. Regular medical follow-up is then essential to monitor liver health.

Cirrhosis and Hepatocellular Carcinoma

In the long term, chronic liver inflammation can lead to fibrosis, which can itself progress to cirrhosis. Cirrhosis is a severe and irreversible alteration of the liver structure. It strongly increases the risk of developing liver cancer, called hepatocellular carcinoma. Monitoring chronic HBs antigen carriers mainly aims to prevent these complications.

Inactive HBs Antigen Carrier State

Some people are positive for HBs antigen but have neither symptoms nor liver inflammation (normal transaminases). This is called inactive carriage. These people have a very low viral load. Although the risk of complications is low, medical follow-up is still necessary, as virus reactivation is possible.

Occult Hepatitis B

More rarely, a person can be infected with HBV without HBs antigen being detectable by standard tests. This is called occult hepatitis B. The diagnosis then relies on the detection of viral DNA in the blood. This situation mainly concerns immunocompromised people.

Practical Advice in Case of a Positive Result

A positive result requires a medical consultation. Here are some general tips and an overview of follow-up.

Typical Follow-up Schedule

• Initial diagnosis: Consultation with a specialist (hepatologist, gastroenterologist) is recommended for a complete assessment.
• Acute Hepatitis B: A follow-up check at 6 months is crucial to verify if HBs antigen has disappeared.
• Chronic Hepatitis B: Follow-up is generally every 6 to 12 months and includes blood tests (viral load, transaminases) and a liver ultrasound.

Lifestyle Recommendations

• Diet:
  • Prioritize a diet rich in fruits, vegetables, and fiber.
  • Limit fatty, sugary, and ultra-processed foods.
• Alcohol: Complete cessation of alcohol consumption is strongly recommended as it is toxic to the liver.
• Physical activity: Regular activity helps maintain a healthy weight and reduce inflammation.
• Medications: Avoid self-medication. Always seek your doctor’s advice, as some medications can be harmful to the liver.

When to Consult a Specialist Without Delay?

• Upon the first discovery of a positive HBs antigen.
• If you are pregnant.
• In case of symptoms such as jaundice, extreme fatigue, or abdominal pain.
• Before starting treatment that weakens the immune system (chemotherapy, biotherapy).

Frequently Asked Questions About HBs Antigen

Does a positive HBs antigen mean I am contagious?

Yes, in general, the presence of HBs antigen indicates that the virus is active and that you can transmit it. Transmission occurs through blood, unprotected sexual intercourse, and from mother to child during childbirth.

What is the difference between HBs antigen and anti-HBs antibodies?

HBs antigen is part of the virus (current infection). Anti-HBs antibody (anti-HBs Ab) is the defense produced by your body. Having only anti-HBs antibodies means you are immune (due to vaccination or a cured old infection).

Can you have a false positive for HBs antigen?

This is very rare with current techniques, but possible. Very recent vaccination (less than one month) can sometimes cause a falsely positive and transient result. A confirmation test is always performed in case of doubt.

Does hepatitis B treatment make HBs antigen disappear?

Current treatments for chronic hepatitis B are very effective in controlling virus multiplication (making viral load undetectable), but they rarely lead to the disappearance of HBs antigen. Achieving this goal, called “functional cure,” is the aim of current research.

I am vaccinated, do I still need to get an HBs antigen test?

The vaccine is very effective but not 100% foolproof. In specific situations (symptoms, risk of exposure before vaccination), a doctor may deem it useful to check. However, for a properly vaccinated and immune person, this test is generally not necessary.

Additional resources

• To deepen your knowledge, click here.
• To extend your knowledge and decipher other markers, more articles are available here.

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