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We are currently experiencing longer than normal turnaround times for serology test results. We are working to resolve this issue and apologize for any inconvenience.

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Syphilis – Serology

Syphilis – Serology

Consistent with O. Reg. 671/92 of the French Language Services Act, laboratory testing information on this page is only available in English because it is scientific or technical in nature and is for use only by qualified health care providers and not by members of the public.

This page provides serological testing information for syphilis at Public Health Ontario (PHO). The causative agent of syphilis is Treponema pallidum. For information regarding other testing options, refer to the following PHO webpages:

Updates:

  • Addition of an interpretation table.
*Uncontrolled print copy. Valid only on day of print: 21 Nov 2024.
Testing Indications Specimen Collection and Handling Requisitions and Kit Ordering Test Frequency and Turnaround Time (TAT) Test Methods Reporting

Testing Indications

Syphilis serology testing is indicated for routine diagnosis of suspected syphilis infections and treatment monitoring of syphilis cases. Screening is recommended for individuals presenting with risk factors, and pregnant people in their first trimester or at the first prenatal visit. Repeat screening in pregnancy should be considered for individuals with ongoing or high risk. For more information on syphilis screening, refer to the Canadian Guidelines on Sexually Transmitted Infections.

If ordering as part of a prenatal screening, see Prenatal Serology. For initial syphilis testing on newborns, it is recommended that maternal serum also be submitted with a separate requisition.

Acceptance/Rejection Criteria

  • Donor testing is not available through PHO’s laboratory. Specimens from patients being screened as potential donors (e.g. organ, tissue, cells, fertility, etc.) should be referred to a laboratory that performs donor screening assays. Specimens received for donor screening at PHO’s laboratory will be rejected.
  • Specimens received more than 7 days post collection will not be tested.
  • Cord blood samples are not acceptable.

Specimen Collection and Handling

Specimen Requirements

Test Requested Required Requisition(s) Specimen Type Minimum Volume Collection Kit

Syphilis

Serum

1.5 mL

Serum Separator Tubes (SST)

Submission and Collection Notes

1

Complete all fields of the requisition form, including:

  • Test(s) requests and reason for testing
  • Patient setting, specimen type and site
  • Relevant clinical information
2

Label the specimen container(s) with the patient’s first and last name, date of collection, and one other unique identifier such as the patient’s date of birth or Health Card Number. For additional information see: Criteria for Acceptance of Patient Specimens. Failure to provide this information may result in rejection or testing delay.

3

Submit centrifuged serum separator tubes (SST) for serological assays.

4

One FULL 5 ml SST is required for testing a combination of hepatitis viruses, HTLV, syphilis and rubella. If a full tube cannot be drawn, submit two tubes.

5

Do NOT submit glass tubes.

Limitations

  • Heat-inactivated, hemolysed, icteric, lipemic or microbial contaminated serum is not recommended for testing.
  • The screen test may be falsely negative in early infection.
  • Liquid anticoagulants may have a dilution effect resulting in lower concentrations for individual patient specimens.

Storage and Transport

Place specimen tube in biohazard bag and seal. Place completed General Test Requisition in the pouch at the front of the biohazard bag.

Specimen tubes should be stored at 2-8°C following collection and centrifugation, and should be shipped to PHO’s laboratory on ice packs within 3 days of collection. If delayed shipping is anticipated, remove serum from clot and store frozen at -20°C or colder, and ship on dry ice.

All clinical specimens must be shipped in accordance to the Transportation of Dangerous Good Act.

Requisitions and Kit Ordering

Test Requisition

Requisition form to be completed by authorized health care providers for ordering clinical tests at PHO’s laboratory.

339 KB
Updated 5 Sep 2024

Test Frequency and Turnaround Time (TAT)

Syphilis screening is performed daily Monday to Friday.

Syphilis confirmatory testing is performed daily Monday to Friday.

Turnaround time is up to 3 business days from receipt at PHO’s laboratory for non-reactive specimens and up to 6 business days for reactive specimens.

Test Methods

PHO follows a reverse algorithm for syphilis testing.

  1. Syphilis Screening: Chemiluminescent microparticle immunoassay (CMIA) – a qualitative immunoassay that detects treponemal antibodies (IgG and IgM) to Treponema pallidum. This test does not distinguish between IgG and IgM.
  2. Syphilis Confirmatory:
    1. Rapid plasma reagin (RPR) - a semi-quantitative flocculation assay that detects non-treponemal antibodies to cardiolipin-lecithin- cholesterol (Reagin antibodies).
    2. Treponema pallidum particle agglutination (TP.PA) - a qualitative gelatin particle agglutination assay that confirms antibodies (IgG and IgM) to Treponema pallidum. This test does not distinguish between IgG and IgM. TP.PA reactivity is used as an aid in the diagnosis of current/past syphilis infection.

Algorithm

Diagram 1. Syphilis serology testing algorithm

Diagram 1. Syphilis Serology Testing Algorithm. This diagram describes the testing algorithm for syphilis serological tests. Serum specimens submitted for syphilis testing are screened by CMIA. Non-reactive CMIA specimens are reported as non-reactive and no confirmatory testing will be performed. Reactive CMIA specimens will be tested for RPR screening, if RPR screening is reactive, quantitative value (titer) will be reported, and no further testing is performed. Specimens that are non-reactive for RPR screening will be tested for TPPA if the patient has no previous TPPA reactive.

Interpretation

Syphilis serology results must be interpreted with the clinical, treatment, and exposure history of the individual. Syphilis staging cannot be done with serology results alone. The following table provides interpretations and recommendations for the most common results.

Syphilis Serology Result Interpretations This table organizes case results in four subject headings (labelled from left to right): Serology Screening Test CMIA, Confirmatory Test RPR, Confirmatory Test TPPA, and Possible Interpretation and Recommendations. Case results are reported as per the headings and collated in table form for easier viewing of the interpretation.

Serology Screening Test (CMIA)1 Confirmatory Test (RPR) Confirmatory Test (TPPA)1 Possible Interpretations/ Recommendations

 

 

Non-reactive

 

 

Not tested

 

 

Not tested

  • No confirmatory testing is performed if syphilis screen result is non-reactive.
  • Early incubating syphilis can be non-reactive before antibodies have developed.
  • If not done already, repeat syphilis serology testing is recommended in 4 weeks for individuals suspected of syphilis infection or re-infection.
  • Patients suspected of congenital syphilis should be referred to an infectious diseases or a paediatric specialist.   

 

Reactive

 

Reactive (titer)

 

Not tested

  • Consistent with recent or prior syphilis infection.
  • If not done already, repeat syphilis serology testing is recommended in 4 weeks for individuals suspected of syphilis infection or re-infection.

 

 

Reactive

 

 

Reactive (titer)

 

 

Reactive/
Non-reactive/
Indeterminate


Patients ≤18 months

  • TPPA testing is completed even with a reactive RPR.
  • Suggestive of congenital infection.
  • Patients suspected of congenital syphilis should be referred to an infectious diseases or a paediatric specialist. Consider repeat serology at recommended intervals.2

 

 

 

Reactive

 

 

 

Non-reactive

 

 

 

Reactive/
Previous Reactive

  • Consistent with recent or prior syphilis infection.
  • If not done already, repeat syphilis serology testing is recommended in 4 weeks for individuals suspected of syphilis infection or re-infection.

Patients ≤18 months

  • Does not rule out congenital infection.
  • Patients suspected of congenital syphilis should be referred to an infectious diseases or a paediatric specialist. Consider repeat serology at recommended intervals.2

 

 

 

 

Reactive

 

 

 

 

Non-reactive

 

 

 

 

Non-reactive

  • Results consistent with false reactive screening test.
  • Rare alternate interpretations include early syphilis, previously treated, or late latent syphilis.
  • If not done already, repeat syphilis serology testing is recommended in 4 weeks for individuals suspected of syphilis infection or re-infection.

Patients ≤18 months

  • Inconclusive syphilis serology.
  • Patients suspected of congenital syphilis should be referred to an infectious diseases or a paediatric specialist.

 

 

Reactive

 

 

Non-reactive

 

 

Indeterminate

  • Inconclusive syphilis serology results
  • Possible interpretations include false positive, or early, old treated or untreated syphilis.
  • If not done already, repeat syphilis serology testing is recommended in 4 weeks for individuals suspected of syphilis infection or re-infection.
  • Patients suspected of congenital syphilis should be referred to an infectious diseases or a paediatric specialist.

1Maternal antibody transfer can be present in infants for up to 18 months.
2https://cps.ca/en/documents/position/congenital-syphilis

Reporting

Results are reported to the physician, authorized health care provider (General O. Reg 45/22, s.18), or submitter as indicated on the requisition.

Specimens that are positive for syphilis are reported to the Medical Officer of Health as per the Ontario Health Protection and Promotion Act.

*Uncontrolled print copy. Valid only on day of print: 21 Nov 2024.
contact lab

Contact Laboratory Customer Service

Microbiology and Laboratory Services

customerservicecentre@oahpp.ca

Updated 11 Sep 2023
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