Indications for Testing
Serology is a useful tool to determine immunization status or previous exposure to infectious agents, but testing should not be a barrier to the vaccination of individuals, especially those who are at a high risk for exposure to vaccine-preventable disease. The CDC offers guidance for the use of serology to determine immunization status for individuals with complete medical records, those with missing or incomplete medical records, pregnant women, and healthcare workers (HCWs).
Those with Complete Medical Records
Individuals who have complete medical records should not receive serology testing to determine immunization status. If applicable, these individuals should follow all CDC-recommended vaccination schedules for any missing vaccinations.
Those from Outside U.S. or with Incomplete Records
Individuals with incomplete, missing, or questionable medical records (eg, children adopted from outside the United States, recent immigrants) may require revaccination or serology testing. In general, vaccinations should be repeated in cases of uncertainty, but judicious use of serology can determine which vaccinations are needed for these individuals.
Validation of vaccination status based on a person’s country of origin or vaccination records alone is often difficult. Individuals with written documentation that lists vaccination type, dates of administration, intervals between doses, and age at the time of vaccination that are generally consistent with the CDC recommendations are more likely to be protected from exposure to vaccine-preventable diseases. However, because of variable vaccination standards and quality across countries, vaccination status is difficult to guarantee. The CDC provides vaccine-specific guidance in the Evaluation and vaccination of persons vaccinated outside of the U.S. who have no (or questionable) vaccination records.
All pregnant women should be evaluated for evidence of immunity to rubella and varicella zoster virus during every pregnancy. Women without evidence of immunity to rubella and varicella should be vaccinated immediately after delivery.
For all other diseases, the CDC recommendations for the use of serology for pregnant women with unknown vaccination status are the same as for all adults with unknown status. Serology may be used to determine immunization status, but appropriate revaccination is recommended.
Because HCWs are at risk for exposure to many serious diseases, the CDC provides specific vaccination requirements for these individuals. To comply with the CDC’s requirements, an HCW may provide medical documentation or up-to-date serology results that prove prior vaccination. Serology is not required, although in some situations it may be more cost-effective than revaccination of individuals with incomplete or missing records. If serology does not show evidence of prior immunization, or if the HCW has uncertain immunization status, revaccination according to established procedures is required. After a vaccination series is completed, serology can be used to determine if a patient has responded to the vaccine.
Individuals with Needlestick Exposure
In some cases, serology can be used as an evaluation tool after a needlestick injury. If the vaccination status of an exposed individual is unknown, serology can aid in the determination of appropriate medical management. However, if postexposure prophylaxis is deemed necessary, it should begin without waiting for the test results.