Syphilis testing results

[Lily Dalke]

Hi all,

 

I was taught in school that to test for syphilis, you should do an initial screen with a non-treponemal antibody test (VDRL or RPR). Positive results should be confirmed with a treponemal test (syphilis antibody test, FTA-ABS). Most sources confirm this approach, including UpToDate:

http://www.uptodate.com/contents/diagnostic-testing-for-syphilis?source=search_result&search=syphilis&selectedTitle=2%7E150

 

Last time I cared for a patient with syphilis, I realized that for some reason Woodhull does the tests in reverse - that is, we use the treponemal syphilis antibody test as our initial screening test, and then we do reflex to the non-treponemal RPR, with further reflex to the treponemal FTA.  The problem with this is that the treponemal tests remain positive for a person's lifetime, so they are not good at differentiating between active vs past infection.

 

Now I have had 2 pts with positive syphilis antibody tests and negative RPR tests. Most sources are unclear what to do with these results - if the RPR had been done first (as intended) the syphilis antibody test never would have been run. The UpToDate link listed above has the following advice from the CDC:

 

"The CDC has published some suggestions for diagnostic management for clinicians who receive these discordant results [7,8]:

• If there is a history of previously treated syphilis, the non-reactive nontreponemal test indicates that active infection is unlikely and no further treatment or testing is warranted.
• For persons without a history of treatment, the CDC recommends that a second, different treponemal test (preferably the Treponema pallidum-Particle agglutination assay [TP-PA]), should be performed [7]. If the TP-PA test is nonreactive, and the patient has no symptoms or behavioral risk to suggest syphilis, the clinician may decide that no further evaluation or treatment is indicated; this approach is supported by one prospective study of more than 21,000 patients undergoing syphilis screening in a low prevalence setting [31].
• If the second treponemal test is reactive, clinicians should discuss the possibility of infection and offer treatment to patients who have not been previously treated. Such patients are unlikely to be infectious (unless history or physical examination suggests otherwise) and should be treated for late latent infection, even though they do not meet standard surveillance criteria [8]."

In the case of my 2 patients, the first had no memory of ever being treated. The second had been treated. In both cases we treated them for latent syphilis x3 doses of penicillin. In the case of the second patient (who has now been treated twice), I am unsure how to evaluate the outcome of this second treatment. Her lab results are the same as they were before treatment (except her FTA went from "reactive" to "minimally reactive"). I'm also unsure, given the above information, that she should have been treated at all.

 

Here is another source that indicates that we should not treat if the syphilis Ab test is positive and the RPR is negative: www.wardelab.com/edit_17_2.html

 

Curious to know your thoughts/reactions/wisdom.

 

Thanks,

 

Lily

[Feldman Rebecca]

I am trying to figure this exact thing out. Lets try and address with Dr Thomas. I would like to request the Rpr to be done first.
Rebecca

[Lily Dalke]

Yes! I don't know why we don't do the RPR first - anyone have the background on this? What's the best way of addressing it with Dr. Thomas?

[Martha Rodorigo]

Hi -

I would reference CDC and/or NYS dept of health - their recommendations and present it to Dr Thomas/Kastell

I can be happy to help with this - let me know

Marhta

[Lily Dalke]

I started writing my letter to Dr. Thomas & Dr. Kastell tonight - and then found this in the 2010 CDC guidelines for STIs:

 

"Some clinical laboratories and blood banks have begun to screen samples using treponemal tests, typically by EIA or chemiluminescence immunoassays (201,202). This strategy will identify both persons with previous treatment for syphilis and persons with untreated or incompletely treated syphilis. The positive predictive value for syphilis associated with a treponemal screening test result might be lower among populations with a low prevalence of syphilis.

Persons with a positive treponemal screening test should have a standard nontreponemal test with titer performed reflexively by the laboratory to guide patient management decisions. If the nontreponemal test is negative, then the laboratory should perform a different treponemal test (preferably one based on different antigens than the original test) to confirm the results of the initial test. If a second treponemal test is positive, persons with a history of previous treatment will require no further management unless sexual history suggests likelihood of re-exposure. Those without a history of treatment for syphilis should be offered treatment. Unless history or results of a physical examination suggest a recent infection, previously untreated persons should be treated for late latent syphilis. If the second treponemal test is negative, further evaluation or treatment is not indicated."

Source: http://www.cdc.gov/std/treatment/2010/genital-ulcers.htm#syphilis

So according to these guidelines, Woodhull's sequence of tests is acceptable - since we do the treponemal Syphilis Ab test with reflex to the non-treponemal RPR with reflex to the treponemal FTA-ABS