Is there a Tdap (Tetanus, diphtheria, and pertussis) titer test?

Tdap Titer Testing Availability

There is no FDA-licensed serologic test for pertussis immunity in the United States, but tetanus and diphtheria titers can be measured in specific situations—though routine serologic testing is not recommended by the CDC, which instead advises age-appropriate revaccination for persons with unknown or questionable vaccination records. 1

Pertussis (the "P" in Tdap)

• No standardized titer test exists for pertussis immunity assessment 1
• The CDC does not endorse serologic testing for pertussis because no FDA-licensed serologic assay is available for routine diagnostic or immunity assessment 1
• Single-sample serologic assays for pertussis cannot reliably differentiate immune responses from recent disease, remote disease, or vaccination 1
• The CDC recommends only culture and PCR as pertussis diagnostic tests, not serologic testing 1

Tetanus and Diphtheria (the "Td" in Tdap)

Serologic testing is available but not routinely recommended:

• Tetanus and diphtheria antibody testing can be considered in specific situations, particularly when vaccination history is unknown or uncertain 1
• Protective antibody levels are ≥0.1 IU/mL for both tetanus and diphtheria 1, 2
• If both tetanus and diphtheria antitoxin levels are >0.1 IU/mL, previous vaccination with tetanus and diphtheria toxoid-containing vaccines is presumed 1

Clinical Approach Algorithm

For persons with unknown or uncertain immunization history:

1. Default approach: Proceed directly to age-appropriate revaccination with Tdap rather than ordering serologic testing 1
2. Alternative approach (limited situations): Serologic testing for tetanus and diphtheria is listed as an option only for DTaP in children, not routinely for Tdap in adults 1
3. If serologic testing is performed and shows protective levels (>0.1 IU/mL for both tetanus and diphtheria), only a single dose of Tdap is needed, not a full series 1

Key Caveats

• Even though tetanus and diphtheria titers can technically be measured 3, 2, the CDC's recommended approach prioritizes revaccination over serologic testing in most clinical scenarios 1
• The lack of a pertussis titer means you cannot assess immunity to all three components of Tdap through serology alone 1
• Research shows that antibody responses to Tdap vaccination occur relatively rapidly, with levels beginning to increase by days 5-7 and approaching peak levels by day 14 4