Can a titer test be used to determine MMR immunity in a patient with unknown vaccination status?

Using Titer Tests to Determine MMR Immunity in Patients with Unknown Vaccination Status

Yes, a titer test can be used to determine MMR immunity in patients with unknown vaccination status, and is specifically recommended by ACIP as an alternative approach to revaccination. 1

Evidence-Based Approach to MMR Immunity Assessment

When faced with a patient who has unknown or questionable MMR vaccination status, the Advisory Committee on Immunization Practices (ACIP) provides two clear options:

1. Recommended approach: Revaccination with MMR vaccine
2. Alternative approach: Serologic testing for IgG antibodies to measles, mumps, and rubella 1

This guidance is explicitly outlined in Table 14 of the ACIP general recommendations on immunization.

When to Consider Titer Testing vs. Direct Vaccination

Situations where titer testing is appropriate:

• When documentation of vaccination is unavailable
• When evaluating presumptive evidence of immunity
• When assessing immunity in high-risk settings (e.g., healthcare workers)
• When the cost-effectiveness of testing vs. vaccination favors testing

Situations where direct vaccination is preferred:

• During outbreaks or when rapid protection is needed
• Before international travel where immediate protection is desired
• When serologic testing is not cost-effective or readily available 2

Interpretation of Titer Results

When interpreting MMR titer results:

• Positive titer: Indicates immunity to the respective disease
• Negative or equivocal titer: In individuals with no documented vaccination, indicates susceptibility and need for vaccination
• Important caveat: For individuals with 2 documented doses of MMR vaccine, ACIP does not recommend an additional dose even if titers are negative or equivocal 2

Special Considerations for Healthcare Personnel (HCP)

For healthcare workers specifically, the ACIP provides additional guidance:

• Presumptive evidence of measles immunity includes:

  • Written documentation of vaccination
  • Laboratory evidence of immunity (positive titer)
  • Laboratory confirmation of disease
  • Birth before 1957 (with some exceptions) 1

• For HCP with 2 documented doses of MMR vaccine or other acceptable evidence of immunity to measles, serologic testing for immunity is not recommended 2

Pitfalls and Caveats

1. Documentation trumps serology: ACIP clearly states that "documented age-appropriate vaccination supersedes the results of subsequent serologic testing" 2

2. Cost considerations: Prevaccination antibody screening should only be performed if considered cost-effective by the medical facility 2

3. Timing issues: Antibody titers may wane over time, but this doesn't necessarily indicate lack of protection in previously vaccinated individuals

4. Vaccine safety: The MMR vaccine has an excellent safety profile with rare serious adverse events:

   • Anaphylaxis: approximately 1.0–3.5 occurrences per million doses
   • Thrombocytopenia: three to four cases per 100,000 doses 2

Algorithm for Approaching Unknown MMR Status

1. Check for documentation of prior MMR vaccination
2. If documentation exists: No further action needed if 2 doses are documented
3. If no documentation or incomplete vaccination:
   • Option A: Administer MMR vaccine (preferred for rapid protection)
   • Option B: Check MMR titers first, then vaccinate if negative/equivocal
4. If titers are checked and negative/equivocal: Administer MMR vaccine
5. If vaccination is chosen: Two doses separated by at least 28 days are recommended for adults with no evidence of immunity 2

Remember that the goal is to ensure immunity to these potentially serious diseases, and both approaches (direct vaccination or titer testing followed by vaccination if needed) are acceptable based on ACIP guidelines.