In a patient with a known severe hypersensitivity reaction to tetanus toxoid, how should a tetanus skin test be performed and how should prophylaxis be managed based on the test result?

Tetanus Skin Testing in Patients with Severe Hypersensitivity Reactions

If a patient has a documented severe hypersensitivity reaction (e.g., anaphylaxis or generalized urticaria) to tetanus toxoid, intradermal skin testing with appropriately diluted tetanus toxoid should be performed before discontinuing tetanus vaccination entirely, as most patients with reported anaphylactic symptoms will test negative and can safely receive future doses. 1

Performing the Skin Test

Test Methodology and Interpretation

• Use intradermal injection of appropriately diluted tetanus toxoid for skin testing, as this is the validated method recommended by ACIP guidelines. 1

• Avoid using undiluted tetanus toxoid for skin testing, as mild, nonspecific skin-test reactivity to undiluted toxoid is fairly common and does not represent true allergy. 1

• Distinguish between immediate hypersensitivity (IgE-mediated) and delayed cutaneous hypersensitivity, as most vaccinees develop inconsequential delayed cutaneous hypersensitivity to the toxoid that does not contraindicate future vaccination. 1

• Do not perform routine skin testing in patients without a history of severe systemic reactions, as intradermal injection of concentrated IgG solutions often causes localized inflammation that can be misinterpreted as a positive allergic reaction. 2

Evidence from Clinical Studies

• In one landmark study of 95 persons with histories of anaphylactic symptoms following tetanus toxoid, 94 were nonreactive on intradermal testing and tolerated further tetanus toxoid challenge without incident; even the one person with immediate erythema and induration on skin testing tolerated a full IM dose without adverse effects. 1

• Reactive responses to immediate skin tests are exceedingly rare (less than 1%) in patients with reported adverse reactions to tetanus toxoid, and challenge patients rarely suffer adverse reactions. 3

Management Based on Skin Test Results

If Skin Test is Negative

• Proceed with tetanus toxoid vaccination using standard wound management protocols, as a negative intradermal test indicates the patient can safely receive future doses. 1

• For patients with ≥3 previous doses and clean, minor wounds, administer tetanus toxoid-containing vaccine (Tdap preferred) only if ≥10 years since last dose; no TIG needed. 4

• For patients with ≥3 previous doses and contaminated/tetanus-prone wounds, administer tetanus toxoid-containing vaccine (Tdap preferred) if ≥5 years since last dose; no TIG needed. 4

If Skin Test is Positive (True IgE-Mediated Allergy)

• If a contraindication to tetanus-toxoid-containing preparations exists and the patient has not completed a primary series, give only passive immunization with TIG 250 units IM for wounds that are neither clean nor minor. 1

• Do not administer tetanus toxoid to patients with confirmed IgE-mediated hypersensitivity, as this represents a true contraindication. 1

• Consider graded dosing (desensitization) protocols in rare cases where tetanus vaccination is absolutely necessary despite confirmed allergy, using a multi-step schedule with the tetanus toxoid preparation to which the patient is least sensitive. 5

Special Diagnostic Considerations

• IgE and IgG antibodies to tetanus toxoid can persist for at least 5 years in patients with true allergic reactions, requiring evaluation by skin and/or in vitro tests before subsequent treatment. 6

• Basophil activation testing (BAT) may be useful when skin tests are negative but clinical suspicion remains high, particularly when the vaccine was administered with other drugs and the causative agent is unclear. 7

• IgE antibodies in allergic patients recognize two proteins derived from tetanus toxoid (150 kDa and 50 kDa), corresponding to intracellular and extracellular forms of tetanus neurotoxin. 6

Critical Clinical Pearls

• Local side effects alone do not preclude continued tetanus toxoid use—only severe systemic reactions (generalized urticaria, anaphylaxis, neurologic complications) constitute contraindications. 1

• Distinguish Arthus-type reactions from IgE-mediated anaphylaxis: Arthus reactions occur 2-8 hours post-injection with severe local reactions, fever, and malaise, whereas anaphylaxis occurs within minutes. 1

• Patients with Arthus-type reactions should not receive tetanus toxoid more frequently than every 10 years, even for emergency wound management, as they typically have very high serum tetanus antitoxin levels. 1

• Three patients with vesicular eruptions at immunization sites were found to have delayed hypersensitivity to mercury (thimerosal), not to tetanus toxoid itself—test vaccine components separately if indicated. 3

• When both TIG and tetanus toxoid are indicated, use separate syringes and separate anatomic sites to prevent interference with the immune response. 1, 4