#medstudenttwitter A review of syphilis testing
1/ Scenario 1: You are seeing a patient in clinic and obtain syphilis screening of HCM. For screening, a nontreponemaltest (RPR or VDRL) are usually sent first. What is the sensitivity of the RPR testing?
1/ Scenario 1: You are seeing a patient in clinic and obtain syphilis screening of HCM. For screening, a nontreponemaltest (RPR or VDRL) are usually sent first. What is the sensitivity of the RPR testing?
2/ RPR has on overall sens of 91, spec 95 but decreased sensitivity in primary syphilis (86%) RPR sens> VRDL (sens 78%). Nontreponemal can have false – in primary syphilis due to antibody formation or the prozone effect. 
3/ What about false +? Infections, pregnancy, and SLE are some common causes of false + RPR. See table linked below:
aafp.org/afp/1999/0415/…
aafp.org/afp/1999/0415/…
4/ The RPR is +. The patient mentions that he was treated for syphilis 1 year prior. At that time, his RPR titer was 1:64. No RPR was sent after treatment. Which of the following values are consistent with a past infection?
5/After treatment, RPR should ⬇️ at least 4fold. It will often become - w/ time. Specific treponemal antibodies are usually + for life. Some labs perform reverse screening w/ the treponemal test 1st (FTA-ABS/TP-PA). This ⬆️ sensitivity but more false +. ncbi.nlm.nih.gov/pmc/articles/P…
6/ Scenario 2: You are now admitting a patient with a palmar rash (check at @thecurbsiders graphic on syphilis symptoms below). Concerned for secondary syphilis, you send an RPR which is + with a + confirmatory test.
7/The patient mentions worsening headaches and sensitivity to light. An LP shows 11 WBC (L pred), 2 RBC, protein 50. CSF VDRL is negative. The sensitivity of CSF VDRL is:
8/Here is a good summary chart of neurosyphilis testing from the NEJM. CSF VRL only has a sensitivity of between 30-75 and is not sufficiently sensitive to r/u neurosyphilis when high suspicion. A CSF FTA-ABS has high sens (99-100) but poor specificity (50-70).
9/The FTA-ABS comes back + and you decide to treat for neurosyphilis. The patient has a history of anaphylaxis to penicillin. What do you do?
10/In pts with neurosyphilis, IV penicillin is strongly preferred (limited evidence for doxy/ceftriaxone). In other type of syphilis, doxycycline or ceftriaxone can be used w/ PCN allergy.
Assuming a sens of 75%, would have a neg likelihood ratio of .25, which means negative VDRL will only ⬇️ post test prob by 25-30%. With a sensitivity of 50%, LR=.5 which ⬇️ post test prob by only 15%.
