Anti-HBs Titre Interpreter
Anti-HBs Titre Interpreter
Read a quantitative anti-HBs result after hepatitis B vaccination: the 10 mIU/mL threshold, what a waned titre in a documented responder means, and what to do at each level.
Anti-HBs after vaccination
Titre + context → actionAnti-HBs 42 mIU/mL, taken 6 weeks after the third dose of a primary course, in an immunocompetent healthcare worker
Reading a vaccine-response titre
- ≥10 mIU/mL
- the protective threshold. mIU/mL and IU/L are the same number
- Responder
- anti-HBs ≥10 mIU/mL 1–2 months after a complete ≥3-dose course — a status, not a current measurement
- Non-responder
- anti-HBs <10 mIU/mL after two complete courses, six doses in total
- Waning
- a fall below 10 in a documented responder. Immune memory persists; protection does not lapse
- Challenge dose
- one vaccine dose, with anti-HBs retested 1–2 months later, to reveal memory in someone vaccinated remotely
- Timing
- a titre taken outside the 1–2 month window after the last dose cannot establish responder status
Worked example
Anti-HBs 42 mIU/mL, taken 6 weeks after the third dose of a primary course, in an immunocompetent healthcare worker
The sample is 1–2 months after the final dose, so it is a valid post-vaccination response test
42 mIU/mL is at or above 10 → seroprotected, and this person is a documented vaccine responder
42 is below 100, so UK Green Book practice would add one further dose and a booster at five years; CDC practice would not
Record the value and the date — responder status once documented is permanent, and a lower titre years from now will not undo it
What the same number means in four different contexts
| Anti-HBs | Context | Interpretation | Action |
|---|---|---|---|
| 8 mIU/mL | 1–2 months after a first complete course | Failed primary response | Check HBsAg and anti-HBc, then give a second complete course and retest |
| 8 mIU/mL | Documented past result ≥10 | Waned titre in a protected person | None. Immune memory persists |
| 8 mIU/mL | 1–2 months after a second complete course | Vaccine non-responder | Confirm not infected; manage as susceptible; two doses of HBIG after exposure |
| 8 mIU/mL | No documented history | Uninterpretable | Challenge dose, retest 1–2 months later |
| 42 mIU/mL | 1–2 months after a complete course | Seroprotected, documented responder | Record it permanently |
Post-exposure management after a percutaneous or mucosal exposure
| Exposed person | Source HBsAg positive or unknown | Notes |
|---|---|---|
| Documented responder (anti-HBs ≥10 recorded at any time) | No post-exposure prophylaxis | “No postexposure prophylaxis for HBV is necessary, regardless of the source patient’s HBsAg status” — today’s titre is irrelevant |
| Documented non-responder (after 6 doses) | Two doses of HBIG | First as soon as possible after exposure, second one month later. No further vaccine |
| Vaccinated, response never tested | Test the exposed person’s anti-HBs and the source’s HBsAg; manage on the results | The reason to document a post-vaccination titre in the first place |
| Unvaccinated | HBIG plus start the vaccine course | Vaccination should begin at the same visit |
Who needs post-vaccination serologic testing at all
| Group | Test 1–2 months after the final dose? |
|---|---|
| Healthcare and public safety personnel with blood exposure risk | Yes |
| Infants born to HBsAg-positive women, or to women of unknown status | Yes |
| Haemodialysis patients | Yes — and annual testing thereafter, with a booster when anti-HBs falls below 10 |
| Immunocompromised persons, including HIV and stem cell transplant recipients | Yes |
| Sex partners of HBsAg-positive persons | Yes |
| Everyone else vaccinated routinely | No — routine post-vaccination testing is not recommended |
Why a titre below 10 in a documented responder is not a loss of protection
Anti-HBs after hepatitis B vaccination is a quantitative question with a single well-established threshold. “Immunocompetent adults and children who have vaccine-induced anti-HBs levels of ≥10 mIU/mL 1–2 months after having received a complete, ≥3-dose HepB vaccine series are considered seroprotected and deemed vaccine responders.” Both halves of that sentence matter: the number, and the timing. A sample taken outside the 1–2 month window after the last dose cannot establish responder status, because by then the titre is already falling.
And it does fall — in everyone, including people who responded beautifully. This is where the commonest misreading happens. Once a person has a documented anti-HBs of 10 mIU/mL or more after a complete course, they are a responder for life, and a later result of 4 mIU/mL does not undo that. Protection is carried by immunological memory rather than by circulating antibody: on exposure, memory B cells mount an anamnestic response faster than the virus establishes infection. CDC states that “revaccination is not generally recommended for persons with a normal immune status” and that “protection against acute symptomatic and chronic HBV infection persists for 30 years or more among immunocompetent persons who originally responded”. The clearest practical expression of this is the post-exposure rule: a documented responder needs no prophylaxis after a needlestick, “regardless of the source patient’s HBsAg status”, and nobody rechecks their titre first.
The mirror image of that is the patient with no documentation, who is extremely common because routine post-vaccination testing is not recommended outside the listed risk groups. A low anti-HBs in someone vaccinated fifteen years ago is genuinely uninterpretable: “because vaccine-induced anti-HBs wanes over time, testing HCP for anti-HBs years after vaccination might not distinguish vaccine nonresponders from responders”. The way out is a challenge dose — one dose of vaccine, anti-HBs retested 1–2 months later — which reveals memory if it is there. It usually is: among people vaccinated 9 to 22 years previously with anti-HBs below 10, between 69.2% and 96.4% responded to a single dose. Most “non-responders” found by late testing are nothing of the kind.
True non-response is defined by failing twice. Anti-HBs below 10 mIU/mL 1–2 months after a second complete course — six doses in total — makes someone a vaccine non-responder, and about half of those who fail the first course respond to the second, so the second course is always worth giving before applying the label. Two things must then happen. HBsAg and anti-HBc are checked, because unrecognised chronic infection presents exactly as apparent vaccine failure; the hepatitis B serology interpreter sets out how those markers read together. And the person is managed as susceptible, which means two doses of hepatitis B immune globulin after a significant exposure, the first as soon as possible and the second a month later, with no further vaccine. Finally, one geographical caution: the UK Green Book uses three bands rather than two, treating 10–100 mIU/ml as a response that still warrants one additional dose and a booster at five years, and reserving “adequate” for 100 and above. A titre of 42 is a responder in both systems and gets an extra dose in only one of them. This supports a clinician’s judgement rather than replacing it. It is arithmetic on the figures entered, and it knows nothing about the patient in front of you.
Frequently asked questions
What anti-HBs level indicates protection after hepatitis B vaccination?
10 mIU/mL or above, measured 1–2 months after the final dose of a complete course of at least three doses. That result defines a vaccine responder, and mIU/mL and IU/L are the same number.
My anti-HBs has fallen below 10. Am I still protected?
If you have a documented result of 10 mIU/mL or more after a complete course, yes. Antibody wanes in everyone but immune memory persists, and CDC does not recommend revaccination for immunocompetent people who originally responded. After a needlestick, a documented responder needs no post-exposure prophylaxis regardless of the source’s HBsAg status.
What defines a hepatitis B vaccine non-responder?
Anti-HBs below 10 mIU/mL 1–2 months after a second complete vaccine course — six doses in total. About half of those who fail a first course respond to a second, so the label should not be applied after three doses. Non-responders should be tested for HBsAg and anti-HBc, and if uninfected managed as susceptible.
When should anti-HBs be tested after vaccination?
1–2 months after the final dose. Earlier and the response is incomplete; later and a falling titre can no longer establish responder status. Routine testing is recommended only for healthcare personnel, infants of HBsAg-positive mothers, haemodialysis patients, immunocompromised people and sex partners of HBsAg-positive people.
What should be done when a titre is low and there is no documented vaccination history?
Give a challenge dose of vaccine and retest anti-HBs 1–2 months later. Among people vaccinated 9 to 22 years previously with anti-HBs below 10 mIU/mL, 69.2% to 96.4% responded to a single dose, which shows that most such results represent waning rather than non-response.
Why do UK and US guidance give different anti-HBs bands?
They divide the same threshold differently. CDC uses one cut at 10 mIU/mL: at or above it you are a responder. The UK Green Book adds a second cut at 100 mIU/ml, treating 10–100 as a response that should receive one additional dose at the time and a booster at five years. A titre of 42 mIU/mL is a responder under both, and gets an extra dose under only one.
Related calculators
References
- Schillie S, Murphy TV, Sawyer M, et al. CDC guidance for evaluating health-care personnel for hepatitis B virus protection and for administering postexposure management. MMWR Recomm Rep. 2013;62(RR-10):1–19.
- Schillie S, Vellozzi C, Reingold A, et al. Prevention of hepatitis B virus infection in the United States: recommendations of the Advisory Committee on Immunization Practices. MMWR Recomm Rep. 2018;67(1):1–31.
- UK Health Security Agency. Hepatitis B: the green book, chapter 18. August 2024.
- Terrault NA, Lok ASF, McMahon BJ, et al. Update on prevention, diagnosis, and treatment of chronic hepatitis B: AASLD 2018 hepatitis B guidance. Hepatology. 2018;67(4):1560–99.
Medical Disclaimer: The tools and content provided here are for educational and reference purposes only. They are not intended to substitute for professional medical advice, diagnosis, or treatment. Clinical decisions should always be based on the comprehensive assessment of a qualified healthcare professional.