Skip to content
MedExams

Syphilis testing: nontreponemal and treponemal

7 ASCP MLS practice questions on Syphilis testing: nontreponemal and treponemal, part of Immunology. The first 7 are below; the first 5 with answers and explanations (tap Show answer after you have chosen), the rest in Learn with a free account.

  1. Question 1 · Hard

    A 38-year-old man was treated with benzathine penicillin for secondary syphilis 3 years ago. His RPR fell from 1:128 at diagnosis to nonreactive by 12 months and was still nonreactive at a check 14 months ago. A recent sexual partner has now been diagnosed with primary syphilis; he has no symptoms. The laboratory uses the reverse sequence algorithm, and today his treponemal chemiluminescence immunoassay (CIA) is reactive, with a signal-to-cutoff ratio of 18 (reactive at 1.0 or more). Which result will show whether he has been reinfected?

    1. AA TP-PA on the same sample
    2. BThe CIA signal-to-cutoff ratio
    3. CA quantitative RPR compared with his last
    4. DA treponemal IgM immunoassay
    Show answer

    Answer: C · A quantitative RPR compared with his last

    Treponemal antibodies usually stay detectable for life after treatment, so in a person with treated syphilis the reactive CIA is expected and says nothing about a new infection. Nontreponemal titers reflect disease activity: his RPR became nonreactive after treatment, so a newly reactive RPR, or a fourfold rise over his last titer, would show reinfection. In the reverse algorithm, a reactive treponemal screen is always followed by an RPR, titrated when reactive, and here that titer is the only informative result. A TP-PA would simply be reactive again, and the CIA ratio is not used to judge disease activity. Because his partner has primary syphilis, he should also be treated presumptively even if today's RPR is nonreactive.

    • A: TP-PA stays reactive after treatment, so it cannot separate old from new infection.
    • B: The signal-to-cutoff ratio is not used to judge disease activity or reinfection.
    • D: Treponemal IgM tests are not recommended for adults and do not reliably show reinfection.

  2. Question 2 · Medium

    In the reverse sequence syphilis algorithm shown, the test that belongs in the dashed box is:

    Figure: MedExams
    Flowchart: a treponemal EIA or CIA screen; nonreactive leads to no serologic evidence of syphilis, reactive leads to a quantitative RPR. A reactive RPR leads to syphilis, current or past; a nonreactive RPR leads to a dashed box marked with a question mark, whose reactive result means past or untreated late latent syphilis and whose nonreactive result means a likely false-positive screen.
    1. ATP-PA, a different treponemal assay
    2. BThe same treponemal EIA, repeated
    3. CA VDRL, as a second nontreponemal test
    4. DCSF VDRL to look for neurosyphilis
    Show answer

    Answer: A · TP-PA, a different treponemal assay

    In the reverse sequence, a reactive treponemal EIA or CIA is followed by a quantitative RPR. When the RPR is nonreactive the two disagree, and a second treponemal test built on different antigens, preferably TP-PA, settles it. A reactive TP-PA means past syphilis or untreated late latent infection; a nonreactive one means the screen was most likely a false positive. A VDRL detects the same nontreponemal antibodies as the RPR, repeating the same EIA would reproduce its false positive, and CSF VDRL is used only when neurosyphilis is suspected.

    • B: Repeating the same assay would reproduce a false-positive screen.
    • C: VDRL detects the same nontreponemal antibodies as the RPR, so it adds nothing.
    • D: CSF VDRL is for suspected neurosyphilis, not for resolving discordant serum results.

  3. Question 3 · Medium

    In the traditional syphilis algorithm, a reactive RPR (titer 1:2) is followed by a nonreactive TP-PA. The RPR result is most likely:

    1. AEvidence of untreated latent syphilis
    2. BEvidence of a recent reinfection
    3. CEvidence of treated past syphilis
    4. DA biological false positive
    Show answer

    Answer: D · A biological false positive

    A reactive nontreponemal test with a nonreactive treponemal test usually means a biological false positive. Cardiolipin antibodies appear in pregnancy, autoimmune disease such as SLE and antiphospholipid syndrome, injection drug use, older age and acute infections. In treated past syphilis it is the treponemal test that stays reactive, not the RPR alone. If very early infection is suspected, both tests can be repeated in 2 to 4 weeks.

    • A: Latent syphilis would give a reactive treponemal test.
    • B: Reinfection occurs in someone whose treponemal test is already reactive.
    • C: After treatment the treponemal test usually stays reactive for life.

  4. Question 4 · Hard

    A 68-year-old man is screened before surgery with the reverse algorithm. He has no history of syphilis, no symptoms and no known exposure. Results: treponemal chemiluminescence assay reactive; RPR nonreactive; TP-PA nonreactive. The best interpretation is:

    1. ALikely false-positive treponemal screen
    2. BPast syphilis that was adequately treated
    3. CEarly primary syphilis before the RPR turns positive
    4. DLate latent syphilis needing treatment
    Show answer

    Answer: A · Likely false-positive treponemal screen

    In the reverse algorithm, a reactive treponemal immunoassay with a nonreactive RPR is resolved with a second treponemal test that uses different antigens, usually TP-PA. A nonreactive TP-PA means the first result was most likely a false positive, especially in a person at low risk. CDC guidance is that no further testing or treatment is needed in that setting. Had the TP-PA been reactive, the result would mean past treated or untreated latent syphilis, depending on the history.

    • B: Past treated syphilis would also leave the TP-PA reactive.
    • C: He has no lesion or exposure, so early primary infection is very unlikely.
    • D: Latent syphilis would give a reactive TP-PA.

  5. Question 5 · Easy

    The RPR card test uses which antigen?

    1. ACardiolipin-lecithin-cholesterol with charcoal
    2. BRecombinant T. pallidum proteins
    3. CWhole Treponema pallidum cells
    4. DSheep red cells coated with T. pallidum
    Show answer

    Answer: A · Cardiolipin-lecithin-cholesterol with charcoal

    The rapid plasma reagin test is a nontreponemal flocculation test. Its antigen is cardiolipin with lecithin and cholesterol, the same base as the VDRL antigen, with charcoal particles added so the flocculation can be seen without a microscope. It detects reagin, antibody to lipoidal material released from damaged host cells and from the treponeme. Because it is not specific for T. pallidum, a reactive result needs a treponemal test.

    • B: Recombinant proteins are used in treponemal immunoassays.
    • C: Whole treponemes are used in the FTA-ABS test, a treponemal test.
    • D: Coated red cells were used in the treponemal MHA-TP test.

  6. Question 6 · Hard

    A 24-year-old woman has a rash on her palms and soles. Her qualitative RPR on undiluted serum is read as nonreactive, but the reaction looks rough and granular. The treponemal immunoassay is reactive. What should the lab do next?

    1. AReport the RPR as nonreactive
    2. BRequest a VDRL test on cerebrospinal fluid
    3. CRepeat the RPR on serial dilutions of the serum
    4. DRepeat the treponemal test after heating the serum

    Answer and explanation in LearnFree account

More Immunology questions

Answer them one by one, keep your score and see your weak topics in Learn. Signed-out visitors try 25 per exam; sign in with Google to see them all.

Study Immunology