How should I interpret hepatitis B serology showing anti‑HBs 0.599 (cut‑off 0.152, positive), anti‑HBc IgM 0.378 (cut‑off 0.725, negative) and anti‑HBc IgG 0.377 (cut‑off 1.392, negative)?

Hepatitis B Serology Interpretation

Primary Interpretation

This patient has isolated anti-HBs positivity (vaccine-induced immunity or passive antibody transfer) with negative anti-HBc markers, indicating either successful hepatitis B vaccination response or recent hepatitis B immune globulin (HBIG) administration—not natural HBV infection. 1

Serologic Pattern Analysis

Your patient's results show:

• Anti-HBs: 0.599 (cut-off 0.152) = POSITIVE – Indicates presence of surface antibody 1
• Anti-HBc IgM: 0.378 (cut-off 0.725) = NEGATIVE – Rules out acute infection 1
• Anti-HBc IgG: 0.377 (cut-off 1.392) = NEGATIVE – Rules out past natural infection 1

Clinical Significance

The combination of positive anti-HBs with negative anti-HBc (both IgM and IgG) definitively indicates vaccine-induced immunity rather than natural infection recovery. 1 According to the Advisory Committee on Immunization Practices, persons who respond to hepatitis B vaccine are positive only for anti-HBs, whereas persons who recover from natural HBV infection are positive for both anti-HBs and anti-HBc. 1

Key Differentiating Feature

• Vaccine responders: Anti-HBs positive, anti-HBc negative (this patient's pattern) 1
• Natural immunity: Anti-HBs positive, anti-HBc positive, HBsAg negative 1

Protective Immunity Status

This patient is immune to hepatitis B infection if the quantitative anti-HBs level is ≥10 mIU/mL. 1 The CDC guidelines state that anti-HBs concentration ≥10 mIU/mL after vaccine series completion indicates immunity. 1

Critical Action Required

• Obtain quantitative anti-HBs titer immediately to confirm protective immunity (≥10 mIU/mL threshold) 1, 2
• If anti-HBs <10 mIU/mL, the patient is susceptible and requires revaccination 1

Alternative Explanation (Less Likely)

Anti-HBs can also be detected for 4–6 months following HBIG administration, which would produce this identical serologic pattern. 1 If the patient received HBIG within the past 6 months (post-exposure prophylaxis, liver transplant, or newborn of HBsAg-positive mother), this represents passive antibody transfer rather than active immunity. 1

Clinical History to Obtain

• Recent hepatitis B vaccination (within past 6 months) 1
• Recent HBIG administration (within past 6 months) 1
• Occupational or sexual exposure requiring post-exposure prophylaxis 1

Critical Pitfall to Avoid

Do not assume this patient has had natural HBV infection—the negative anti-HBc definitively excludes past infection. 1 Some clinicians mistakenly interpret any positive anti-HBs as indicating prior infection, but the absence of anti-HBc is the key differentiator. 1 Natural infection always generates anti-HBc, which persists for life in most individuals. 1

No Further HBV Testing Required

If vaccination history is confirmed and quantitative anti-HBs is ≥10 mIU/mL, no additional hepatitis B serologic testing is needed. 1, 2 This patient does not require:

• HBsAg testing (already immune) 1
• HBV DNA testing (no evidence of infection) 1
• Repeat anti-HBc testing (definitively negative) 1

Management Algorithm

1. Verify vaccination history – Confirm completion of 3-dose hepatitis B vaccine series 1
2. Order quantitative anti-HBs titer – Must be ≥10 mIU/mL for protection 1, 2
3. If anti-HBs ≥10 mIU/mL: Patient is immune, no further action needed 1
4. If anti-HBs <10 mIU/mL: Administer single booster dose and recheck titer in 1–2 months 1
5. If no response to booster: Complete revaccination with 3-dose series and recheck titer 1