A 25-year-old man comes to the primary care clinic for routine sexually transmitted infection screening. He is currently asymptomatic and has no history of genital lesions. The clinic's affiliated laboratory recently switched to the 'reverse sequence algorithm' for syphilis screening to handle high testing volumes more efficiently. Assuming the initial screening test is reactive, and the reflex test is non-reactive, arrange the following laboratory assays in the correct chronological order they would be performed to complete the diagnostic workup.
- 1Treponemal enzyme immunoassay (EIA)
- 2Quantitative rapid plasma reagin (RPR) test
- 3Treponema pallidum particle agglutination (TP-PA) assay
Answer
The correct order is: 1) Treponemal enzyme immunoassay (EIA), 2) Quantitative rapid plasma reagin (RPR) test, 3) Treponema pallidum particle agglutination (TP-PA) assay.
The correct sequence reflects the chronological progression of the reverse sequence algorithm for syphilis testing. High-volume laboratories begin with an automated treponemal test (EIA or CIA). A reactive result prompts a reflexive nontreponemal test (RPR) to assess disease activity. Because the vignette specifies a non-reactive second test (discordant results), a second, different treponemal assay (TP-PA) must be performed to confirm whether the initial EIA was a true positive (seen in early, late, or previously treated syphilis) or a false-positive screening result.
Step-by-Step Solution
Key Concept
The reverse sequence algorithm for syphilis screening starts with a treponemal EIA, reflexes to a nontreponemal RPR if reactive, and requires a second treponemal test (TP-PA) if the RPR is non-reactive to resolve discordant results.
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