What does a negative hepatitis B surface antigen (HBsAg) screen indicate?

What Does a Negative HBsAg Screen Mean?

A negative HBsAg test indicates the person does not have detectable hepatitis B surface antigen in their blood, which most commonly means they are not currently infected with hepatitis B virus, though this single test alone cannot definitively rule out all forms of HBV infection. 1

Primary Interpretations of Negative HBsAg

A negative HBsAg result can represent several distinct clinical scenarios that require additional testing to differentiate:

Never Infected or Vaccinated

• The person has never been exposed to HBV and has never been vaccinated, making them susceptible to future infection 2
• This is confirmed when both anti-HBc and anti-HBs are also negative 2

Resolved Past Infection with Natural Immunity

• The person previously had HBV infection but has cleared the virus and developed protective immunity 1, 2
• This pattern shows HBsAg negative, anti-HBs positive (≥10 mIU/mL), and anti-HBc positive 1, 2
• Anti-HBc remains detectable for life after natural infection, serving as a permanent marker of past exposure 1, 2

Vaccine-Induced Immunity

• The person has been successfully vaccinated against HBV 2, 3
• This shows HBsAg negative, anti-HBs positive (≥10 mIU/mL), but anti-HBc negative (distinguishing it from natural immunity) 2, 3

Window Period of Acute Infection

• During acute HBV infection, there is a brief "window period" when HBsAg has disappeared but anti-HBs has not yet appeared 1
• During this window, HBc IgM antibody is the only detectable marker and confirms acute infection 1
• This window typically occurs 4-6 months after initial infection 1

Critical Caveat: Occult HBV Infection

A negative HBsAg does NOT always mean absence of HBV infection. Occult HBV infection (OBI) is characterized by undetectable HBsAg but detectable HBV DNA in serum or liver tissue 2, 4

• OBI occurs in approximately 10% of persons who are HBsAg-negative but anti-HBc-positive 5
• In blood donor studies excluding large-scale screening, OBI rates reach 10% among anti-HBc-positive individuals 5
• OBI has significant implications for disease transmission, particularly in blood transfusion, organ transplantation, and immunosuppression settings 4, 5
• Patients with OBI can still develop hepatocellular carcinoma despite negative HBsAg 4

Essential Next Steps Based on Clinical Context

For Screening in Asymptomatic Individuals

• Measure anti-HBc (total) and anti-HBs simultaneously with HBsAg to determine complete immune status 2, 6
• If anti-HBc is positive (regardless of anti-HBs status), the person has been exposed to HBV 2
• If both anti-HBc and anti-HBs are negative, the person is susceptible and should receive hepatitis B vaccination 2, 3

For Patients with Isolated Anti-HBc Positivity (HBsAg Negative, Anti-HBs Negative)

• This pattern suggests either resolved infection with waning anti-HBs or occult chronic infection 2
• Test HBV DNA to detect occult hepatitis B, especially in immunocompromised individuals or those from high-prevalence regions 2
• False-positive anti-HBc results are more common in low-prevalence populations 2

For Patients Starting Immunosuppressive Therapy

• All patients with any anti-HBc positivity face HBV reactivation risk with immunosuppression 6
• Measure HBV DNA before starting immunosuppressive therapy, even if HBsAg is negative 6
• The American Society of Clinical Oncology recommends monitoring HBsAg and ALT every 3 months during anticancer therapy for patients with past HBV infection (HBsAg-negative, anti-HBc-positive) 1

For Acute Hepatitis Evaluation

• If clinical hepatitis is present with negative HBsAg, test for anti-HBc IgM to detect acute HBV infection during the window period 1, 7
• Anti-HBc IgM can identify 20% of patients with apparent "non-A, non-B hepatitis" as actually having acute hepatitis B 7
• Restrict IgM anti-HBc testing to those with clinical hepatitis or epidemiologic exposure, as false positives occur in asymptomatic persons 6

Common Pitfalls to Avoid

• Never assume a single negative HBsAg test rules out all HBV infection, particularly in immunocompromised patients, those from endemic areas, or patients requiring immunosuppression 2, 5
• Do not rely on HBsAg testing alone for blood donor screening or pre-transplant evaluation, as this misses occult HBV infection 8, 5
• Recognize that transient HBsAg positivity can occur for up to 18 days after hepatitis B vaccination, which is clinically insignificant 2
• Anti-HBs levels can decline over time after natural infection, leaving only anti-HBc detectable, but this still reflects past infection with residual immunity 2