What does a reactive Hepatitis B surface antibody (HBsAb) test result indicate?

From the Guidelines

HBsAb reactive indicates immunity to hepatitis B virus, requiring no treatment or further action, as confirmed by the 2018 update by the Infectious Diseases Society of America and the American Society for Microbiology 1. This immunity could have developed either from previous hepatitis B vaccination or from a resolved hepatitis B infection. Some key points to consider include:

• The presence of HBsAb indicates recovery from and immunity to HBV infection, as a result of either natural infection or vaccination, as stated in the 2018 guide to utilization of the microbiology laboratory for diagnosis of infectious diseases 1.
• If this was found during routine screening, no additional testing is typically needed unless there are other abnormal liver tests or symptoms.
• This immunity is generally considered lifelong after natural infection, though vaccine-induced immunity may wane over time in some individuals.
• For those with vaccine-induced immunity who are at ongoing high risk of exposure (like healthcare workers), antibody levels can be checked periodically, and a booster dose may be recommended if levels fall below 10 mIU/mL, as suggested by general medical practice. The presence of these antibodies means your immune system can recognize and fight the hepatitis B virus if you're exposed to it in the future, effectively preventing infection. In terms of laboratory diagnosis, the 2018 update provides guidance on the optimal specimens, transport time, and diagnostic procedures for hepatitis A and E, but for hepatitis B, the focus is on the interpretation of serologic markers like HBsAb, HBsAg, and HBc antibodies, as discussed in the context of hepatitis B infection diagnosis and management 1.

From the Research

HBsAB Reactive Interpretation

• HBsAB reactive refers to the presence of both hepatitis B surface antigen (HBsAg) and hepatitis B surface antibody (HBsAb) in a patient's blood [ 2, 3, 4 ].
• This phenomenon can occur in patients with chronic hepatitis B, as well as those with resolved HBV infection [ 2, 3 ].
• The presence of HBsAb is generally considered protective against HBV reactivation, but the level of protection may depend on the titre of HBsAb [ 3 ].

Clinical Implications

• Patients with HBsAB reactive results should be closely monitored for HBV reactivation, particularly if they are undergoing anti-B-cell therapy or direct-acting antiviral therapy for hepatitis C [ 2, 3 ].
• Antiviral prophylaxis may be recommended for patients with HBsAg-positive results, while regular monitoring of HBV DNA and preemptive antiviral therapy may be suitable for patients with resolved HBV infection [ 2 ].
• The presence of baseline HBsAb-specific B cells may predict HBsAg or HBeAg seroconversion in patients with chronic HBV infection [ 5 ].

HBV Reactivation Risk

• The risk of HBV reactivation depends on various factors, including the balance between viral replication and the host immune response [ 2 ].
• Patients with HBsAg-positive results are considered to be at high risk of HBV reactivation, while those with resolved HBV infection are also at risk [ 2 ].
• The incidence of HBV reactivation in patients with resolved HBV infection can range from 9% to 24% [ 2 ].

Diagnostic and Therapeutic Considerations

• All patients should be screened for HBV markers, including HBsAg, anti-HBc, and anti-HBs, before initiating anti-B-cell therapy [ 2 ].
• Antiviral therapy, such as entecavir, may be effective in reducing HBV DNA levels and improving liver function in patients with chronic HBV infection [ 4 ].
• The transition to HBeAg-negative chronic infection is associated with reduced cccDNA transcriptional activity, which may contribute to the control of viral replication [ 6 ].