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Zorluk: OrtaOrdering Laboratory Tests

A 32-year-old man presents to the primary care clinic requesting comprehensive sexually transmitted infection (STI) screening. He recently entered a new relationship and wants to ensure he is healthy. He has no current symptoms, and a detailed physical examination reveals no oral, genital, or anal lesions, nor any rashes. The clinic's laboratory employs the reverse sequence diagnostic algorithm for syphilis screening. For this patient, the initial screening test returns a reactive result, while the subsequent reflex test returns a nonreactive result, prompting a third laboratory test.

Arrange the following laboratory tests in the exact chronological sequence they would be performed for this patient according to the reverse sequence algorithm.

  1. 1Treponemal-specific enzyme immunoassay (EIA)
  2. 2Quantitative rapid plasma reagin (RPR) test
  3. 3Treponema pallidum particle agglutination (TP-PA) assay

Cevap

The correct sequence of tests is: Treponemal-specific enzyme immunoassay (EIA), followed by Quantitative rapid plasma reagin (RPR) test, and finally Treponema pallidum particle agglutination (TP-PA) assay.
The reverse sequence algorithm for syphilis begins with an automated treponemal test (EIA or CIA). If this initial test is reactive, the sample must be reflexed to a nontreponemal test (RPR or VDRL) to evaluate for active disease and establish a baseline titer. If the results are discordant (i.e., reactive EIA but nonreactive RPR), a second, different treponemal test, most commonly the TP-PA assay, is required to determine whether the initial EIA was a false positive or if the patient has treated or late latent syphilis.

Adım Adım Çözüm

1
Identify the initial screening test used in the reverse sequence algorithm.
The reverse sequence algorithm begins with an automated treponemal test, typically an enzyme immunoassay (EIA) or chemiluminescence immunoassay (CIA).
Laboratories increasingly favor this algorithm because treponemal immunoassays can be highly automated, saving labor and resources compared to manual nontreponemal testing.
2
Determine the reflex test ordered after a positive initial screen.
A quantitative nontreponemal test, such as the rapid plasma reagin (RPR) test, is ordered next.
While the EIA confirms treponemal exposure, the RPR assesses for active disease and provides a baseline titer to monitor the efficacy of future treatment.
3
Select the final confirmatory test based on the discordant results provided in the vignette.
Since the stem states the reflex test (RPR) was nonreactive, a second treponemal test, such as the Treponema pallidum particle agglutination (TP-PA) assay, must be performed.
A reactive EIA and a nonreactive RPR can represent either a false-positive EIA or a true prior/early infection. The TP-PA assay helps definitively distinguish between these possibilities.

Anahtar Kavram

The reverse sequence algorithm for syphilis testing begins with a treponemal immunoassay, reflexes to a nontreponemal test (such as RPR) if positive, and requires a second distinct treponemal test (such as TP-PA) if the first two tests yield discordant results.
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Ordering Laboratory Tests

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