Anti-HBs, or Hepatitis B Surface Antibody, is a protein produced by the immune system in response to the Hepatitis B virus (HBV). Its presence indicates protection against future Hepatitis B infection. It serves as a key marker of immune status against this common liver infection. Testing for Anti-HBs assesses whether a person has developed immunity from vaccination or recovery from a past infection.
Understanding Anti-HBs
Anti-HBs is an antibody produced by the immune system. It targets the Hepatitis B Surface Antigen (HBsAg), a protein on the virus’s surface. The immune system produces Anti-HBs to neutralize HBsAg, preventing the virus from infecting healthy liver cells.
The body can develop Anti-HBs through two primary mechanisms. One way is through successful vaccination against Hepatitis B, where the vaccine introduces HBsAg to the immune system, prompting it to produce protective antibodies. The other way is as a result of recovering from a natural Hepatitis B infection. When an infected person’s immune system successfully clears the virus, it produces Anti-HBs, which then provides immunity against future infections.
Reasons for Anti-HBs Testing
Healthcare providers order Anti-HBs tests to determine an individual’s immune status to Hepatitis B. Testing is frequently performed after a person has completed the Hepatitis B vaccination series to confirm adequate immunity has developed. This is particularly relevant for healthcare workers and others at high risk of exposure to blood or bodily fluids.
Testing for Anti-HBs also helps confirm recovery from a past Hepatitis B infection. In individuals who have been infected, the presence of Anti-HBs, alongside the absence of HBsAg, signifies that the infection has resolved and immunity has been established. Additionally, it can be part of broader screening panels to assess overall Hepatitis B status.
Deciphering Your Anti-HBs Results
A “positive” or “reactive” Anti-HBs result indicates developed immunity. This protection stems from successful vaccination or a resolved past Hepatitis B infection. A common benchmark for protective immunity is an Anti-HBs level greater than or equal to 10 milli-International Units per milliliter (mIU/mL). Levels significantly above this threshold, such as greater than 100 mIU/mL, suggest a strong immune response. Even if levels decrease over time, an individual may still retain protection due to immune memory.
Conversely, a “negative” or “non-reactive” Anti-HBs result indicates a lack of detectable immunity, meaning the person is susceptible to Hepatitis B infection. In such cases, vaccination or a booster dose may be recommended to establish protection. If a vaccinated individual tests negative, further doses or a re-evaluation of their vaccination status might be necessary.
“Equivocal” or “indeterminate” results, sometimes falling between 5 and 12 mIU/mL, suggest a borderline level of antibodies. These results often warrant retesting or consideration of a booster dose to ensure protective immunity. While rare, it is possible for HBsAg and Anti-HBs to coexist, which typically requires further investigation by a healthcare professional to understand the full Hepatitis B status. Therefore, a healthcare provider will consider all relevant test results and clinical history to provide a complete assessment and recommend appropriate next steps.