The eligibility for blood donation when Hepatitis B antibodies are present depends entirely on the specific type of antibody found. Antibodies are protein markers produced by the immune system, indicating either past exposure to the Hepatitis B virus (HBV) or successful protection. Because the safety of the blood supply is paramount, regulatory bodies must distinguish between antibodies that signify immunity and those that signal a history of infection. The difference between these markers determines whether an individual can safely donate.
Differentiating Hepatitis B Antibodies
Donation eligibility rules are based on three primary markers that appear sequentially following exposure to HBV. The Hepatitis B Surface Antigen (HBsAg) is a protein on the outer coat of the virus, and its presence indicates an active infection, whether acute or chronic. A positive HBsAg result leads to an immediate and permanent deferral from donation.
The Hepatitis B Surface Antibody (HBsAb, or anti-HBs) is the protective antibody, developing after successful vaccination or recovery from natural infection. HBsAb indicates immunity and is generally not a cause for deferral when it is the sole positive marker.
The Hepatitis B Core Antibody (HBcAb, or anti-HBc) is a marker of past exposure to the virus’s core protein. This antibody persists for life, even after the infection has cleared. The presence of HBcAb alone indicates a history of infection and holds significant implication for blood donation eligibility.
Donation Eligibility Following HBV Vaccination
The presence of the protective HBsAb resulting from vaccination does not disqualify a person from donating blood. The vaccine introduces only the surface protein, prompting the immune system to produce HBsAb without causing an actual infection. Therefore, a vaccinated individual will test positive for HBsAb and negative for HBcAb and HBsAg.
A temporary deferral may be imposed immediately following a recent Hepatitis B vaccination. This is because the vaccine can sometimes cause a transient, low-level detection of HBsAg in screening tests, leading to a false-positive result. To avoid this, blood centers generally require a short waiting period, often 14 days, after the most recent dose of the vaccine.
Donation Eligibility Following Past HBV Infection
When antibodies are present due to a past, cleared infection, the eligibility criteria become much more restrictive. If a donor was diagnosed with Hepatitis B at any point, they are typically not eligible to donate blood, even if they have fully recovered and are currently immune. This near-universal deferral is primarily based on the presence of the Hepatitis B Core Antibody (HBcAb).
The presence of the HBcAb signals a past infection and leads to a permanent deferral, regardless of a positive HBsAb indicating recovery. This stringent rule is a preventative measure against occult Hepatitis B infection (OBI). OBI is a rare state where the virus’s genetic material, HBV DNA, remains in the liver or blood at very low levels, often undetectable by standard HBsAg tests.
Although the risk of transmission from an HBcAb-positive, HBsAg-negative donor is extremely low, the theoretical possibility of transmitting OBI through blood transfusion is considered too great a risk to the blood supply. Major regulatory bodies implement permanent deferral for all individuals who test positive for HBcAb.
The Blood Donation Screening Process
Even after a donor is deemed eligible based on their medical history and questionnaire, every unit of donated blood undergoes rigorous laboratory testing before it is released for use. This multi-barrier screening system is designed to catch infectious agents that may be present during the “window period” of acute infection, before antibodies have fully developed.
The screening process for Hepatitis B involves multiple tests, including serological assays for HBsAg and HBcAb, often using enzyme-linked immunosorbent assay (ELISA) technology.
In addition to these antibody and antigen tests, all donations are screened using Nucleic Acid Testing (NAT) to detect the actual genetic material (HBV DNA) of the virus. NAT is highly sensitive and can detect the virus earlier in the infection cycle than traditional serology, significantly reducing the “window period” risk. Any donation that tests reactive for HBsAg, HBcAb, or HBV DNA by NAT is immediately quarantined and discarded, and the donor is notified of the result and deferred from future donation.