Definition

Anti-HBs, or Surface Hepatitis B Antibody, is a specific protein produced by the immune system in response to exposure to the hepatitis B virus. This antibody is a marker of the body’s defense mechanism against hepatitis B infection. Upon encountering the virus, the immune system initiates a response, forming antibodies uniquely designed to target and neutralize hepatitis B.

The specificity of these antibodies arises from the distinct surface protein structure of the hepatitis B virus, known as the surface antigen. This antigen is recognized by the immune system, triggering the production of precise antibodies to combat the virus.

Detecting hepatitis B antibodies in the bloodstream signifies prior exposure to the virus, recovery from infection, or vaccination. The immune system's ability to form these antibodies enables it to recognize and respond more effectively to subsequent hepatitis B infections.

There are two classes of antibodies associated with hepatitis B:

• IgM (Immunoglobulin M): These antibodies are generated early in the infection and typically disappear over time.
• IgG (Immunoglobulin G): These antibodies are produced later and can persist for years, providing long-term immunity, although their levels may gradually decrease over time.

Anti-HBs can be measured through a specific test designed to detect its presence. This test serves various purposes, such as identifying prior exposure to the virus or confirming recovery and immunity following infection. Additionally, it can assess the immune system's response to hepatitis B vaccination, offering insights into the success of the vaccination process. However, routine post-vaccination anti-HBs testing is not generally performed.

Hepatitis B infection primarily targets the liver and can pose risks to both adults and children. Transmission occurs through contact with infected blood, sexual activity, or from mother to fetus via the placenta. Anti-HBs testing can determine whether an individual has had a previous hepatitis B infection, even if no symptoms were present.

Indications

Anti-HBs testing is recommended for individuals at high risk of exposure to and infection with the hepatitis B virus, including:

• Infants born to mothers infected with the hepatitis B virus
• Sexual partners of individuals with hepatitis B infection
• Those with multiple sexual partners in the past six months
• Individuals with a history of sexually transmitted infections (STIs)
• Men who have sex with men (MSM)
• People who use injectable drugs
• Individuals in close contact with hepatitis B-infected persons, such as household members
• Healthcare workers frequently exposed to blood or body fluids from infected individuals
• Residents of or travelers to regions with a high prevalence of hepatitis B
• Inmates or staff working in correctional facilities

Contraindications

There are no specific contraindications for anti-HBs testing. This test is considered safe across all age groups, as it involves the routine collection of blood samples from veins by trained healthcare professionals.

Preparation Before the Test

No special preparation is required prior to the test. However, it is essential to provide accurate information about your symptoms, sexual partners, drug use, occupation, travel history, and place of residence. Sharing this information helps the doctor interpret the test results in context and decide whether additional hepatitis B marker tests are necessary.

Test Procedure

The anti-HBs test involves collecting a blood sample from a vein. The steps are as follows:

1. The healthcare provider will identify the site for blood collection, typically the arm crease.
2. A tourniquet is applied to the arm, and the patient is instructed to clench their fist.
3. The site is cleansed with antiseptic, such as alcohol swabs.
4. After the area dries, a syringe needle is inserted into the selected site.
5. Blood is drawn into a syringe tube, with a volume of approximately 0.3–0.5 mL.
6. The tourniquet is removed, and the needle is withdrawn. The injection site is pressed with an alcohol swab.
7. The blood sample is then sent to the laboratory for analysis.

Normal and Abnormal Values

Anti-HBs levels are measured in mIU/mL (milli-international units per milliliter). The following classifications are based on CDC guidelines:

Table 1. Blood Anti-HBs

Source: CDC (Centers for Disease Control and Prevention)

Normal Values

A normal anti-HBs level is defined as <5.00 mIU/mL or undetectable in the blood. This result indicates a negative test, showing no hepatitis B antibodies or immunity to the virus.

Abnormal Values

An abnormal anti-HBs level is >12.00 mIU/mL, indicating a positive test result. This signifies the presence of antibodies or immunity to the hepatitis B virus.

Indeterminate results occur when anti-HBs levels range between >5.00 and <12.00 mIU/mL. In such cases, the immune status against the hepatitis B virus cannot be conclusively determined.

Results and Recommendations (Further Testing)

Negative

A negative anti-HBs test result indicates that antibodies or immunity against the hepatitis B virus are absent. This suggests that you have never been exposed to or infected by the hepatitis B virus and are currently in good health. However, a negative result can also occur under certain circumstances, such as in chronic hepatitis B infections, cases where the hepatitis B virus has previously infected the body but antibody levels are too low or have started to decline, or during the recovery phase following an infection. For these reasons, doctors may recommend additional hepatitis B marker tests, such as HBsAg and HBcAg tests, to assess the possibility of infection and determine the current infection status. This assessment is further guided by your symptoms, medical history, and a physical test conducted by the physician.

In cases where the anti-HBs test is negative following hepatitis B vaccination, the result suggests that the immune system has not responded to the vaccine, indicating the vaccination was unsuccessful. Further evaluation and additional steps may be necessary in such instances.

Positive

A positive anti-HBs test result signifies the presence of antibodies or immunity against the surface protein of the hepatitis B virus. This outcome may indicate that you are in the recovery phase following a recent or past hepatitis B infection. To determine the current infection status, your doctor may recommend additional tests, such as HBsAg and HBcAB tests. These tests help differentiate between acute and chronic hepatitis B infections. If a positive anti-HBs test result follows hepatitis B vaccination, it indicates that the vaccine was effective and that the body has successfully developed immunity to the hepatitis B virus.

Indeterminate

If the test results are indeterminate, meaning the status of immunity or antibody levels against the hepatitis B virus cannot be determined, a follow-up test is required for clarification.

Consult the Right Doctor

If your anti-HBs test result is positive, consult a general practitioner or an internist immediately. A positive result may indicate hepatitis B infection, necessitating further evaluation and treatment to prevent potential complications associated with the condition.

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