Syphilis – CSF

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Background
This page provides serologic testing information on cerebrospinal fluid (CSF) for the investigation of neurosyphilis at Public Health Ontario (PHO). Neurosyphilis refers to infection of the central nervous system by Treponema pallidum subsp. pallidum (T. pallidum), which may occur at any stage of syphilis infection. The following testing options are available for syphilis: routine serology, CSF-Venereal Disease Research Laboratory (VDRL) testing, and direct fluorescence testing for chancres. This page is for information specific to CSF. For information regarding other testing options, refer to the following PHO webpages:

Updates

Added rejection and acceptance criteria
Added Algorithm
Updated Test Methods
Added Interpretation Table
Reporting: Due to changes in PHO’s and Ontario’s laboratory information systems, cumulative reporting is no longer available

* Copie d'impression non contrôlée. Valide uniquement le jour de l'impression : 01 mai 2025.

Testing Indications

Syphilis VDRL testing on CSF specimens aids in the diagnosis of suspected neurosyphilis and should only be done in individuals with suspected or confirmed syphilis. A diagnosis of neurosyphilis is made using a combination of laboratory tests including, syphilis serology, CSF examinations, and CSF-VDRL with or without clinical manifestations.

CSF-VDRL testing should be considered in individuals (including those who are HIV-positive) with suspected or confirmed syphilis, who:

have neurologic (including ocular and otic/auditory) symptoms or signs
fail to achieve an adequate serologic response to treatment
have tertiary syphilis
are suspected or confirmed to have congenital syphilis

Some experts recommend CSF examinations in HIV-positive individuals with infectious syphilis with an RPR ≥1:32 and CD4 ≤350 cells/µL.

Acceptance/Rejection Criteria

All specimens must be accompanied by a PHO General Test Requisition completed by an authorized health care provider. Requests received with incomplete information on the requisition may be rejected.
CSF will only be accepted for VDRL testing for individuals who have a positive syphilis serology result (historical or current). Requests for CSF-VDRL for individuals with a negative syphilis serology will be rejected.
Xanthochromic, bloody, cloudy CSF samples are not acceptable for testing.
CSF submitted on blood collection tubes with anticoagulant will be rejected.

Specimen Collection and Handling

Specimen Requirements

Test Requested	Required Requisition(s)	Specimen Type	Minimum Volume	Collection Kit
Syphilis-CSF Serology	General Test Requisition	CSF	1.0 ml	Sterile container

Submission and Collection Notes

ALL sections of the General Test Requisition must be completed by authorized health care providers for each specimen submitted to avoid cancellation or delay in testing. Include relevant clinical information (e.g. lesions, neurologic symptoms, etc.)

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.

CSF specimens for syphilis testing can be stored at 2-8°C for 5 days after collection. If longer storage is required, freeze at -20°C.

A blood sample must be submitted for syphilis serology testing if there is no history of a syphilis diagnosis.

Limitations

Blood or serum contamination during collection may produce a false positive result during testing.
Because of the lower sensitivity and potential for cross-reactivity, CSF-VDRL should only be requested for individuals with suspected or confirmed syphilis and should not be used as the sole test for the investigation of neurosyphilis.

Storage and Transport

CSF specimens must be submitted in a leak-proof container and packaged individually. Place the specimen in a biohazard bag and seal. Specimens can be shipped or stored at 2-8°C following collection or frozen if a delay of more than 5 days from collection is anticipated before shipping to PHO.

Shipping of CSF specimens should be done by Transportation of Goods (TDG) certified individuals in accordance with the Transportation of Dangerous Goods Act.

Requisitions and Kit Ordering

Test Frequency and Turnaround Time (TAT)

Syphilis serology for CSF is performed at least 2-3 times per week at PHO.

Turnaround time is up to 5 business days from receipt at PHO.

Test Methods

PHO uses the following tests for syphilis serology testing of CSF:

Screening Test: Venereal Disease Reference Laboratory (VDRL) test – a semi-quantitative flocculation assay that detects non-treponemal antibodies to cardiolipin-lecithin-cholesterol (Reagin antibodies).
Confirmatory tests:
1. Treponema Particle Agglutination (TP.PA) test – a qualitative gelatin particle agglutination assay that confirms antibodies (IgG and IgM) to T. pallidum. This test does not distinguish between IgG and IgM.
2. Fluorescent Treponemal Antibody-Absorption Test (FTA-ABS) – an indirect fluorescent antibody test to confirm antibodies (IgG and IgM) to T. pallidum. This test does not distinguish between IgG and IgM.

Algorithm

PHO follows the traditional algorithm for CSF testing:

All CSF specimens for syphilis serology are screened using VDRL test. VDRL reactive specimens will be tested by TP.PA assay and reported accordingly. CSF-VDRL is highly specific but not sensitive for neurosyphilis. As such, VDRL non-reactive specimens will be tested by FTA-ABS assay and reported accordingly. FTA-ABS is highly sensitive but non-specific for neurosyphilis.

Titers will be provided for VDRL reactive tests.

Interpretation

CSF syphilis serology results must be interpreted with the individual’s signs/symptoms, clinical and treatment history, and other laboratory testing, including syphilis serology and CSF examinations.

The following table provides possible test results with associated interpretations:

VRDL Screen Result	TPPA Result	FTA-ABS Result	Interpretation
Reactive (titre reported)	Reactive	Not Tested	Cerebrospinal fluid serology consistent with recent or prior neurosyphilis, or bloody contamination of CSF.
Reactive (titre reported)	Non-Reactive or Indeterminate	Not Tested	Cerebrospinal fluid serology consistent with recent or prior neurosyphilis, or bloody contamination of CSF.
Non-Reactive	Not Tested	Reactive	Inconclusive syphilis serology of cerebrospinal fluid (CSF).
Non-Reactive	Not Tested	Indeterminate	Inconclusive syphilis serology of cerebrospinal fluid (CSF).
Non-Reactive	Not Tested	Non-Reactive	No serological evidence of neurosyphilis.

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.

Positive specimens are reported to the Medical Officer of Health as per the Ontario Health Protection and Promotion Act.

Due to changes in PHO’s and Ontario’s laboratory information systems, cumulative reporting is no longer available.

References

A Manual of Tests for Syphilis 9th Edition. Edited by S. A. Larsen, V. Pope, R. E. Johnson, E. J. Kennedy Jr. American Public Health Association. Washington, D.C. 1998.
Canadian Public Health Laboratory Network laboratory guidelines for the diagnosis of neurosyphilis in Canada