TP-PAPassive-Particle-Agglutination Test
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Our patient reflects a typical presentation of ocular syphilis in immune competent patient by bilateral posterior invasion of uvea, a positive serology for VDRL-RPR and TP-PA and well response to i.v penicillin treatment.
The CDC and others have recommended TP-PA assays for confirmation, and the high analytical sensitivity of this assay suggests that it would be a suitable choice in a wide range of situations.
The mother's antenatal serologic results were negative for HIV and hepatitis B, and for syphilis by negative VDRL and TP-PA test results.
His VDRL test result was positive at a 1:32 serum dilution, as was TP-PA with 4+ reactivity.
(14) Reactive samples (3.4% overall) were tested with RPR and alternate treponemal testing (TP-PA or FTA-ABS).
To address potential reverse screen FPs, the CDC suggests confirmation of discordant samples using the TP-PA assay: TP-PA reactivity is necessary to rule out an FP.
Among the 3,664 discordant sera, 2,512 were tested with a TP-PA or FTA-ABS, of which 433 (17.2%) were nonreactive, suggesting false-positive EIA treponemal test results.
To evaluate reverse sequence screening in populations with high and low syphilis prevalence and to evaluate the use of TP-PA and FTA-ABS tests for identifying false-positive EIA/CIA screening tests, CDC analyzed syphilis screening data from five clinical laboratories.
La sensibilidad de la prueba TP-PA, utilizada como primera eleccion para el tamizaje, fue de 86% (intervalo de confianza de 95% [IC95%]: 78 a 92%), aunque fue menor en personas seropositivas al VIH que en los seronegativos (55% frente a 77%; P = 0,05).
For those patients, performing a different treponemal test (e.g., TP-PA, TPHA, or FTA-ABS) can help assess whether the treponemal EIA test result was a false positive.
Further testing with FTA-ABS or TP-PA tests on 2,512 of the specimens reactive to the EIA test but nonreactive to the RPR test found 2,079 (83%) specimens reactive to the second treponemal tests (i.e., FTA-ABS or TP-PA).
For instance, in a recent evaluation of 39 dark-field confirmed syphilis cases, VDRL was reactive in 30 (77%) whereas TP-PA was positive in 37 (95%).