Treponemal Test – TPPA

Introduction
The Treponema pallidum particle agglutination (TP-PA) test is a treponemal test (confirmation test) for the serologic detection of antibodies to the various species and subspecies of pathogenic Treponema, the causative agents of syphilis, yaws, pinta, bejel, and endemic syphilis. The test is a passive agglutination procedure based on the agglutination of gel particles sensitized with T. pallidum antigens by antibodies found in the patient's serum (1-3). The test is intended as a confirmatory test to replace the microhemagglutination assay for antibodies to T. pallidum (MHA-TP).

Principle
Serum containing antibodies to pathogenic treponemes react with gel particles sensitized with sonicated T. pallidum, Nichols strain (the antigen), to form a smooth mat of agglutinated gel particles in the microtiter tray well.

If antibodies are not present, the particles settle to the bottom of the tray well, forming a characteristic compact button of unagglutinated particles.

The unsensitized gel particle control well for each serum should also show this compact button, or the absence of agglutination.

The TPPA test is used to confirm the reactive results of a nontreponemal screening test for syphilis, such as the VDRL slide test, or as a diagnostic test in patients with a nonreactive nontreponemal test but with signs or symptoms suggestive of late syphilis

Interpretation of results
1) Read the settling patterns of the gelatin particles using an angled mirror (tray viewer) to visualize the patterns from below - Readings are scored on a scale of – to 2+ agglutination
2) Retest serum with samples with a reading of ±

Boon Ching
TG01