What is the significance of a Hepatitis B surface antibody (HBsAb) quantification of 3.5 mIU/mL?

Hepatitis B Surface Antibody Level of 3.5 mIU/mL Indicates Inadequate Protection

A Hepatitis B surface antibody (anti-HBs) quantification of 3.5 mIU/mL falls below the protective threshold of ≥10 mIU/mL and indicates that you lack adequate immunity against hepatitis B virus infection. 1, 2, 3

Understanding Your Result

Your anti-HBs level of 3.5 mIU/mL means:

• You are NOT protected against hepatitis B infection, as protective immunity requires antibody levels ≥10 mIU/mL 1, 2
• This result indicates you are either unvaccinated, previously vaccinated but failed to develop adequate antibody response, or your antibody levels have waned below protective levels over time 2
• You remain susceptible to HBV infection and require completion of the hepatitis B vaccination series 2

Critical Distinction: Anti-HBs vs HBsAg

Common pitfall to avoid: Do not confuse anti-HBs (antibody TO the surface antigen, which indicates immunity) with HBsAg (the surface antigen itself, which indicates active infection). 2 Your test measured anti-HBs, which reflects your immune response, not the presence of virus.

Immediate Management Required

Step 1: Complete Vaccination Series

You need to receive the complete hepatitis B vaccine series immediately. 2

• Standard schedule: 3 doses at 0,1, and 6 months 2, 3
• Adult dosing: 20 μg per dose (Engerix-B) or 10 μg per dose (Recombivax HB) 2
• Alternative accelerated schedules are available if needed 2

Step 2: Post-Vaccination Testing

Mandatory follow-up: Test your anti-HBs level 1-2 months after completing the vaccine series to confirm you achieved protective immunity (≥10 mIU/mL). 1, 2, 3

• This testing must use a quantitative method that can detect the protective concentration 1
• If anti-HBs remains <10 mIU/mL after the primary series, you will need a second complete 3-dose series 2
• Retest anti-HBs 1-2 months after the second series 2

Special Considerations Based on Your Risk Profile

If You Work in Healthcare

Healthcare personnel require particularly rigorous management: 2

• Post-vaccination testing is essential given occupational exposure risk 1, 2
• If you have documented prior vaccination but unknown antibody response, you should receive one dose of HepB vaccine now, followed by anti-HBs testing 2
• Your institution should ensure timely assessment and postexposure prophylaxis protocols are in place 1

If You Are Immunocompromised

Higher doses or additional doses may be required to achieve protective immunity if you have conditions affecting immune function. 2

Why Levels Below 10 mIU/mL Matter

The threshold of ≥10 mIU/mL is not arbitrary:

• Antibody titers ≥10 mIU/mL are universally recognized as conferring protection against hepatitis B infection 3
• Any level below 10 mIU/mL provides NO protection, regardless of how close it is to the threshold 2
• Your level of 3.5 mIU/mL is significantly below this protective threshold and leaves you fully vulnerable to HBV infection 2

Clinical Context

Hepatitis B infection carries serious consequences including acute massive hepatic necrosis, chronic active hepatitis, cirrhosis, and hepatocellular carcinoma. 3 Up to 90% of infected neonates and 6-10% of infected adults become chronic carriers. 3 The hepatitis B vaccine is recognized as the first anti-cancer vaccine because it prevents primary liver cancer. 3

Action Algorithm

1. Immediately schedule hepatitis B vaccination series (0,1,6 months) 2
2. Complete all three doses on schedule 2, 3
3. Test anti-HBs 1-2 months after final dose 1, 2
4. If anti-HBs ≥10 mIU/mL: You are now protected; no further action needed
5. If anti-HBs <10 mIU/mL: Repeat entire 3-dose series and retest 2
6. Until protected: Avoid high-risk exposures and seek immediate post-exposure prophylaxis if exposed to HBV 1