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Update on syphilis testing via Polymerase Chain Reaction (PCR)

Syphilis testing

The primary method for diagnosing syphilis is through serologic testing. However, in certain situations, it may be appropriate and clinically-indicated to perform one of the direct tests (i.e. swab of a lesion). 

Historically, the only direct tests available were darkfield microscopy and direct fluorescent antibody (DFA). Both of these tests are reliant on specific equipment and expertise to perform and interpret. 

In recent years, the BCCDC Public Health Laboratory (PHL) has been performing Treponema pallidum PCR on lesions collected via swab and stored in special buffer. This buffer has and will continue to be available to anyone requesting it for this purpose. 

More recently, the BCCDC PHL has validated the performance of syphilis PCR using the gonorrhea and chlamydia nucleic acid amplification test (NAAT) kits (i.e., the Aptima®-branded kits). 

What this means for you in your practice

If you see a patient with a genital, anal or oral lesion and you suspect syphilis, consider swabbing the lesion for Treponema pallidum PCR.  Serology should also be done at this time.

For genital or anal lesions, you can also send a slide for DFA (DFA is not appropriate for oral lesions, given the presence of endogenous oral spirochetes; PCR is the only approved direct test for oral lesions).

The sample should be collected by swabbing the lesion.

  • If you only have access to the NAAT kits, swab the lesion with the swab from the kit and place it as you normally would into the container.  There is no need to pour out any fluid from the sample container.  See Figure 1 for examples of the NAAT kits.
  • If you have access to PCR buffer, swab the lesion with a Dacron or polyester swab and break off the tip into the buffer vial.  See Figure 2 an example of the buffer vial and a representative swab type.

Write “Treponema pallidum PCR; Att: Dr. Morshed” on the requisition.

If you have any questions:

  • STI Physician:  604-707-5610
  • STI Nursing Line:  604-707-5603
  • Troy Grennan, Physician Lead, STI Program:  604-707-5606

Figure 1: NAAT Collection Kits

Photo of the Aptima vaginal swab kit
Photo of the Aptima endo-cervical swab kit

Figure 2: PCR Buffer and Swab

Photo of the PCR swab and buffer

Categories: Current practice

Search related content: syphilis, test, PCR, NAAT

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