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Tetanus antitoxoid IgG

Measures antibodies against the tetanus toxin to show whether vaccination still gives you protection.

AI-verified against cited sources. Awaiting expert reviewAlso called Tetanus IgG, Anti-TT IgG, Anti-tetanus IgGLOINC 53935-3

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What it is

Tetanus is a serious illness caused by a toxin made by a bacterium, Clostridium tetani, which can enter the body through cuts and wounds. The tetanus vaccine, often given as part of a combined shot, teaches your body to make antibodies against that toxin. This test measures the amount of those IgG antibodies in your blood, in international units per milliliter (IU/mL). Labs such as Quest treat 0.10 IU/mL or higher as a protective level.

Why it matters

A clinician may order this test to see how well your immune system responded to a tetanus vaccine, often with a blood sample before the vaccine and another about a month after. Because levels fall over time, it can also help when vaccination records are missing. A level below 0.10 IU/mL does not mean you will get tetanus. It is a prompt for your clinician to look at your vaccination history. The result should not be used to decide whether you need antitoxin after an injury, and Quest notes tetanus can still occur in some people with protective levels.

If it’s low

A level below 0.10 IU/mL is under the cutoff that Quest and ARUP use for protection. It often just means antibodies have faded since your last dose. The CDC notes that by 10 years after the last dose most people's levels only approach the minimum protective level, and in a small share of people they fall below it sooner.

Common causes

  • Many years since your last tetanus-containing vaccine dose
  • A vaccine series that was never completed, or no vaccination
  • A weaker response to the vaccine
  • A condition or treatment that weakens the immune system, or an antibody deficiency

What can help

  • Find your vaccination records and share them with your clinician
  • Ask whether a booster dose is recommended for you
  • Ask whether a follow-up level about a month after any booster would be useful

If it’s high

A higher level means more tetanus antibody is in your blood. Levels at or above 0.10 IU/mL are in the range labs call protective. A high result usually reflects a recent vaccine dose.

Common causes

  • A recent dose of a tetanus-containing vaccine (such as Td, Tdap, DTaP or DT)
  • Recent treatment with immune globulin, which carries donor antibodies

Usual ranges

What labs print as the reference range, by who was tested. Ranges differ a little between labs, so the range on your own report is the one your result is judged against.

For adults: 0.1 and above IU/mL. Source: Quest Diagnostics, ARUP Laboratories.

Quest Diagnostics interpretive criteria

  • Below the protective levelbelow 0.1 IU/mL
  • Protective level0.1 and above IU/mL

Serosurvey convention (Greek adult study, 2024)

  • No protection (seronegative)below 0.01 IU/mL
  • Basic protection (low seropositivity)0.01 to under 0.1 IU/mL
  • Full protection0.1 and above IU/mL

What can affect your result

  • Time since your last tetanus-containing vaccine dose
  • Whether you finished the vaccine series
  • Treatment with immune globulin or other blood products
  • The health of your immune system
  • Which lab and method were used
  • Immune globulin or other blood products given before the draw carry donor antibodies and can raise the result without reflecting your own immunity.
  • Results from different labs and methods can differ (Quest uses an immunoassay and ARUP a multiplex bead assay), so compare trends only within the same lab when you can.
  • Grossly hemolyzed, lipemic or icteric samples may be rejected (Quest).

Levels rise within weeks of a vaccine dose (ARUP asks for the follow-up sample one month after the dose) and fall slowly over the years.

When to talk to a clinician

A low level on its own is not urgent. After any deep or dirty wound, puncture or burn, call a clinician or urgent care the same day, whatever this test showed, so they can check your tetanus protection. For jaw stiffness with muscle spasms, or trouble swallowing or breathing, call 911 or your local emergency number.

Questions you could ask

  • Are my vaccination records complete and up to date?
  • Why was this test ordered, and how will the result change what we do?
  • Is a booster dose recommended for me?
  • Could anything about my health or treatment explain a low level?
  • Should we recheck my level about a month after a booster?

Questions people ask

What does 0.10 IU/mL mean?

It is the level that Quest and ARUP treat as the protective threshold for tetanus antibodies. Quest reports 0.10 IU/mL or higher as protective, and ARUP says above 0.1 IU/mL is usually considered protective.

Can I still get tetanus if my level is above 0.10 IU/mL?

It is uncommon, but Quest notes that tetanus can still occur in some people with levels at or above the protective cutoff. This is one reason to get wounds checked even when you think you are protected.

Why do some labs ask for a before and after sample?

Comparing the level before a vaccine dose with the level about a month after shows how strongly your immune system responded. ARUP asks for both samples to be sent together for this reason.

Show the science and sources

Units

  • 1 IU/mL = 1 IU/mL
  • 1 IU/mL = 1000 mIU/mL

Open the Tetanus IgG unit converter

For clinicians and researchers

Tetanus antitoxin IgG is measured against tetanus toxoid. Quest uses an immunoassay (a laboratory-developed test) reported in IU/mL, with 0.10 IU/mL or higher considered protective. ARUP uses a quantitative multiplex bead assay (also a laboratory-developed test) with LOINC 53935-3 and says a concentration above 0.1 IU/mL is usually considered protective. ARUP interprets paired samples drawn before and one month after vaccination: a post-vaccination level under 1.0 IU/mL is a nonresponse; at 1.0 IU/mL or higher, a post/pre ratio under 1.5 is a nonresponse, 1.5 to under 3.0 a weak response and 3.0 or more a good response; if the pre-vaccination level is already above 1.0, a post level above 2.5 IU/mL is usually adequate. The CDC Pink Book states that after a full series essentially all recipients reach levels well above the protective level of 0.1 IU/mL, that levels decline with time, and that routine boosters are recommended every 10 years. A Greek serosurvey of adults used a three-level convention: under 0.01 IU/mL no protection, 0.01 to under 0.1 basic protection and 0.1 or higher full protection. These levels are conventions from a study, and the 0.1 IU/mL cutoff is assay-dependent in practice.

LOINC 53935-3 (primary), 32775-9, 41483-9, 49191-0. Specimen: serum.

Sources

  1. Tetanus Antitoxoid (test code 4862), Quest Diagnostics
  2. Tetanus Antibody, IgG (test 0050535), ARUP Laboratories
  3. Epidemiology and Prevention of Vaccine-Preventable Diseases (Pink Book): Chapter 21, Tetanus, Centers for Disease Control and Prevention
  4. Diphtheria and Tetanus Immunity Status among Greek Adults: Results from a Nationwide Seroprevalence Study, Vaccines (Basel) (2024)

AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. How we build and check these pages.

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