How to Test

Non-treponemal tests detect non-specific antibodies. Non-treponemal antibody tests are done in the laboratory, if one of the treponemal screening tests is reactive. Rapid Antigen Reagin (RPR) testing is the most common confirmatory non-treponemal test, used in the diagnosis of a syphilis infection.

Rapid Antigen Reagin (RPR) testing
Test type	Sample required	Main use	Considerations
Non-treponemal antibody test: detects non-specific antibodies	Venous blood, sent to laboratory* *Refer to your regular lab requirements for sending samples	Confirmatory laboratory tests, with or after treponemal screening test	Interpretation of titre changes can be difficult MUST use SAME laboratory for all serial testing

RPR testing:

• used to monitor the effectiveness of treatment and identify re-infections
• results are reported as a titre:
• titre changes occur over the course of an infection and in response to treatment (as shown in graph below)

RPR Results interpretation

• A 2 titre or 4-fold fall in the RPR (e.g., 1:32 to 1:8) within six months following treatment of infectious syphilis usually indicates adequate response to treatment
• Seek specialist advice if RPR is rising or a 4-fold drop is not achieved by 12 months
• The RPR is unlikely to fall if the baseline titre is very low (as in latent syphilis) and therefore cannot be used in this context to monitor treatment response but can be used to identify new infections.
• A two titre or four-fold rise from a previous RPR result can indicate a new infection (e.g., 1:2 to 1:8).

Testing and logistics:

• Blood tests for syphilis provide a baseline against which to measure future testing, response to treatment and re-infections.
• Blood tests should always be taken if syphilis is suspected and an RPR taken again at the time of commencement of treatment to provide a baseline to measure response to treatment.
• If a PoCT has been conducted and is reactive, venous blood must also be sent to the laboratory for syphilis testing as outlined. The lack of regular transportation to the laboratory is not a reason not to take blood tests.
• Check specific storage and transportation requirements with the local laboratory but in general, specimens that are to be sent some days later can be centrifuged and kept in the fridge and should be transported at 2-8C.

Other non-treponemal syphilis tests

VDRL (Venereal Disease Research Laboratory) test is a non-treponemal test which is currently only used in Australia for testing cerebrospinal fluid (CSF).

A swab should be taken for Syphilis Nucleic Acid Amplification Test (NAAT/PCR) directly from any sore or lesion possibly due to primary or secondary syphilis. A reactive NAAT/PCR test from a lesion confirms infectious syphilis. Indicate on the pathology form where the swab has been taken from (e.g., genital/mouth/peri-anal ulcer). If any anogenital or pharyngeal ulceration is present, request ‘herpes PCR’ on the same swab and collect a separate dry swab for ‘mpox NAAT’. It may also be appropriate to request ‘donovanosis PCR’ on the lesion swab depending on local epidemiology and guidelines.

A blood test should always be taken at the same time for laboratory testing if infectious syphilis is suspected.