Correlation of Treponemal Immunoassay Signal Strength Values with Reactivity of Confirmatory Treponemal Testing

摘要

Automated treponemal immunoassays are used for syphilis screening with the reverse-sequence algorithm; discordant results (e.g., enzyme immunoassay EIA reactive and reactive plasma reagin RPR nonreactive) are resolved with a second treponemal test. We conducted a study to determine automated immunoassay signal strength values consistently correlating with reactive confirmatory treponemal testing. We conducted a cross-sectional analysis of four automated immunoassays (BioPlex 2200 microbead immunoassay MBIA, Liaison chemiluminescence immunoassay CIA, Advia-Centaur CIA, and Trep-Sure EIA) and three manual assays (Treponema pallidum particle agglutination TP-PA, fluorescent treponemal antibody absorption FTA-ABS test, and Inno-LIA line immunoassay). We compared signal strength values of automated immunoassays and positive and negative agreement. Among 1,995 specimens, 908 (45.5) were true positives (= 4/7 tests reactive) and 1,087 (54.5) were true negatives (= 4/7 tests nonreactive). Positive agreement ranged from 86.1 (83.7 to 88.2) for FTA-ABS to 99.7 (99.0 to 99.9) for AdviaCentaur CIA; negative agreement ranged from 86.3 (84.1 to 88.2) for Trep-Sure EIA to 100 for TP-PA (99.6 to 100). Increasing signal strength values correlated with increasing reactivity of confirmatory testing (P 0.0001 for all automated immunoassays by Cochran-Armitage test for trend). All automated immunoassays had signal strength cutoffs corresponding to = 4/7 reactive treponemal tests. BioPlex MBIA and Liaison CIA had signal strength cutoffs correlating with 99 and 100 TP-PA reactivity, respectively. The Advia-Centaur CIA and Trep-Sure EIA had signal strength cutoffs correlating with at least 95 TP-PA reactivity. All automated immunoassays had signal strength cutoffs correlating with at least 95 FTA-ABS reactivity. Assuming that a 95 level of confirmation is adequate, these signal strength values can be used in lieu of confirmatory testing with TP-PA and FTA-ABS.