Each test updates the probability that a real T. pallidum antibody response is present.
The tie-breaker — TP-PA after a positive EIA but non-reactive RPR — is where conditional
independence quietly breaks, because both treponemal assays chase the same antibody.
Pretest probability of infection
Clinical stage — shifts the sensitivities· edited
Stage presets reset the test characteristics
Sensitivities move most across stages; specificities barely. Edit any value below to override.
Your patient's result
The cascade · posterior probability of true infection at each outcome
What the number means
The posterior is P(genuine T. pallidum infection) — active, latent, or past/treated.
It does not by itself separate active from treated disease; that is the work of the RPR
titer plus treatment history.
RPR is modeled independently of EIA (different antibody target — cardiolipin vs. treponemal protein).
EIA and TP-PA are not: their dependence is carried by TP-PA's conditional specificity among
EIA-positives (default 96% vs. % marginal). The gap is why the EIA+/RPR−/TP-PA+ node shows two posteriors.
Defaults are editable literature ballparks for Tp EIA/CIA, RPR, and TP-PA — set them to your lab's
validated performance and local stage mix. Sensitivities move a lot by stage; use the toggle.
Educational tool · not a substitute for clinical judgment, titers, or direct detection (darkfield/PCR).