TPHA Test: Introduction, Principle, Procedure, Result-Interpretation, Clinical Significance, and Keynotes
Table of Contents
TPHA test stands for Treponema pallidum hemagglutination. This is a confirmatory test for syphilis that is caused by a bacterium, T. pallidum. TPHA test is a sensitive indirect hemagglutination test, that detects specific Treponema pallidum antibodies in serum within one hour. It uses in combination, with the VDRL(Venereal Disease Research Laboratory test) or RPR (rapid plasma reagin) and TPHA tests to provide accurate and reliable confirmation of active syphilis infection. No specialized equipment is required and the results are clearly visible and easily interpreted.
TPHA is an indirect hemagglutination assay carried out on microplates for the qualitative and semi-qualitative detection of anti-Treponema pallidum-specific antibodies in human serum. Avian blood cells stabilized and sensitized with a solution of T. pallidum antigen (Nichols strain) agglutinate in the presence of anti-T. Pallidum antibodies, exhibit a typical agglutination pattern (i.e. hemagglutination).
Antigen suspension contains avian red cells sensitized with Nichols strain of Treponema pallidum mixes 1:20 dilution of serum in a microtiter well to make a final dilution of serum 1:80. Now incubate the plate at room temperature for an hour. Finally, observe for hemagglutination.
The upper, left-hand well contains a positive control test. The red cells have had treponemal antigens attached and antibodies in the serum have caused these cells to agglutinate and form a mat across the bottom of the well. These antibodies can be presumed to be specific for Treponemes since otherwise identical red cells that have not had the treponemal antigens attached do not cause hemagglutination, as seen in the bottom, left-hand well. A negative serum test is shown in the center and a patient’s test is on the right as shown above image. This result supports a diagnosis of syphilis. In brief, positive control (PC): is positive, negative control (NC) is negative and the test is also negative as shown in the above footage.
| Test | Primary | Secondary | Latent | Tertiary |
| VDRL | 78(74-87) | 100 | 95(88-100) | 71(37-94) |
| RPR | 86(77-99) | 100 | 98(95-100) | 73 |
| FTA-ABS | 84(70-100) | 100 | 97(97-100) | 94 |
| EIA | 93 | 100 | 100 | – |
| RPR | TPHA | IgM EIA | |
| – | – | – | No syphilis or incubating syphilis |
| – | – | + | Early primary syphilis |
| + | + | + | Primary or secondary |
| + | – | + | Early infection |
| + | + | – | Late secondary or latent syphilis |
| + | – | – | Biological false positive, late syphilis |
| – | + | – | Late infection, treated syphilis, or false positive treponemal test |
| Increasing | + | Increasing | Re-infection, relapse |
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