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Bordetella pertussis toxin (PT) antibody

Test code(s) 37294 (PT IgG and IgA), 37295 (PT IgG)

Question 1. What is the purpose of the Bordetella pertussis toxin (PT) antibody assays?

The purpose of the PT antibody assays is to aid in the diagnosis of B pertussis infection in patients with a persistent cough lasting more than 2 to 3 weeks.

Question 2. Can PT antibody assay results be used to determine if a patient has protective immunity?

No. These assays cannot be used to assess protective immunity to B pertussis, because the specific antibodies and antibody levels that correlate with protection have not been well defined. CDC guidelines do not recommend antibody testing prior to administering the pertussis vaccine.1

Question 3. When should I order a PT antibody assay instead of the B pertussis DNA PCR assay?

The DNA PCR assay, on a nasopharyngeal aspirate or swab, is the preferred test for diagnosing pertussis in individuals with signs and symptoms of pertussis whose cough began within the previous 2 to 3 weeks. Beyond this timeframe, however, the sensitivity of the DNA PCR assay decreases. Thus, if the cough has persisted for more than 2 to 3 weeks, measurement of PT antibodies in serum is the preferred diagnostic test.1,2

Question 4. How are the PT antibody results interpreted?

Results are reported quantitatively as International Units per mL (IU/mL). Values above the reference range suggest recent infection or recent vaccination.

Question 5. When would I need a PT IgA result in addition to a PT IgG result?

PT IgG is the best serologic test for identifying recent pertussis infection in individuals of all ages, with sensitivities and specificities greater than 92% reported in multiple studies.3-7 However, PT IgA is clinically useful in children less than 10 years old to help distinguish recent infection from recent vaccination; within this age group, both PT IgG and PT IgA are increased following infection, but only PT IgG is increased following vaccination.7

Question 6. Why does the assay measure antibodies to PT only, and not antibodies to other pertussis proteins?

PT is the only antigen that is specific for B pertussis, and thus antibodies to PT are found only in association with B pertussis infection. Antibodies to the other major pertussis antigen, filamentous hemagglutinin antigen (FHA), can be found in infections caused by other organisms (eg, other Bordetella species, Mycoplasma pneumoniae, Chlamydophila pneumoniae, Haemophilus influenzae), and thus lack specificity for diagnosis of pertussis infections.3, 5-8

Question 7. What are the age-dependent reference ranges and how were they determined?

The age-dependent reference ranges shown in the table below were determined in a large study employing 140 serum samples from healthy children 4 to 15 years of age, and 500 serum samples from healthy blood donors 16 to 79 years of age. The age-specific reference ranges represent the 90th percentile values for donors within the indicated age groups.

References

  1. Centers for Disease Control and Prevention. Pertussis (whooping cough) diagnosis confirmation. https://www.cdc.gov/pertussis/clinical/diagnostic-testing/diagnosis-confirmation.html. Updated August 17, 2017. Accessed November 28, 2018.
  2. Pawloski L, Plikaytis B, Martin M, et al. Evaluation of commercial assays for single-point diagnosis of pertussis in the US. J Pediatric Infect Dis Soc. 2017;6:e15-e21. doi: 10.1093/jpids/piw035
  3. Van der Zee A, Schellekens JFP, Mooi FR. Laboratory diagnosis of pertussis. Clin Microbiol Rev. 2015;28:1005-1026.
  4. Faulkner A, Skoff T, Cassiday P, et al. Chapter 10: Pertussis. CDC. Manual for the surveillance of vaccine-preventable diseases. Roush SW, Baldy LM, Hall MAK, editors. CDC; Atlanta, GA; 2008. https://www.cdc.gov/vaccines/pubs/surv-manual/chpt10-pertussis.html. Updated November 10, 2017. Accessed November 5, 2018.
  5. Baughman AL, Bisgard KM, Edwards KM, et al. Establishment of diagnostic cutoff points for levels of serum antibodies to pertussis toxin, filamentous hemagglutinin, and fimbriae in adolescents and adults in the United States. Clin Diagn Lab Immunol. 2004;11(6):1045-1053. doi: 10.1128/CDLI.11.6.1045-1053.2004
  6. Watanabe M, Connelly B, Weiss AA. Characterization of serological responses to pertussis. Clin Vaccine Immunol. 2006;13(3):341-348. doi:10.1128/CVI.13.3.341-348.2006
  7. Hendrikx LH, Ozturk K, de Rond LGH, et al. Serum IgA responses against pertussis proteins in infected and Dutch wP or aP vaccinated children: an additional role in pertussis diagnostics. PloS One. 2011;6:e27681. doi:10.1371/journal.pone.0027681
  8. Hodder SL, Cherry JD, Mortimer EA, et al. Antibody responses to Bordetella pertussis antigens and clinical correlations in elderly community residents. Clin Infect Dis. 2000;31(1):7-14. doi:10.1086/313913
This FAQ is provided for informational purposes only and is not intended as medical advice. A clinician’s test selection and interpretation, diagnosis, and patient management decisions should be based on his/her education, clinical expertise, and assessment of the patient.
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Effective 01/25/2019 to present