TPHA test: Introduction, Principle, Procedure, Result Interpretation

TPHA Test: Introduction, Principle, Procedure, Result Interpretation and Clinical Significance

Introduction of TPHA Test

TPHA test stands for Treponema pallidum haemagglutination. This is a confirmatory test for syphilis causative agent Treponema pallidum. TPHA test is a sensitive indirect haemagglutination test, that detects specific Treponema pallidum antibodies in serum within one hour. It uses in combination, the VDRL(Venereal Disease Research Laboratory test) or RPR ( rapid plasma reagin) and TPHA tests provide accurate and reliable confirmation of active syphilis infection.No specialized equipment is required and results are clearly visible and easily interpreted.

Principle of TPHA Test

TPHA(Treponema Pallidum Hemagglutination) 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, exhibiting a typical agglutination pattern(i.e. haemagglutination)

TPHA Test Procedure

Antigen suspension contains avian red cell sensitized with Nichols strain of Treponema pallidum mixes 1:20 dilution of serum in microtitre well to make a final dilution of serum 1:80. Now incubate the plate at room temperature for an hour. Finally, observe for hemagglutination.

Result Interpretations of TPHA Test

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 haemagglutination, 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 figure. This result supports a diagnosis of syphilis. In brief, Positive control (PC): Positive, Negative Control (NC): Negative and test is also negative. For more details watch this clip at-

Keynotes

This is a qualitative method of the TPHA test.
The positive test indicates 1:80 titer.
A quantitative method of the TPHA test is also available. The procedure is nearly the same but there is a need for serial dilution.

Clinical Significance of THPA test

It is a confirmatory test of syphilis.
Sensitivity of Serological Tests in Untreated Syphilis

Key: TPPA stands for Treponema pallidum particle agglutination
FTA-ABS stands for Fluorescent treponemal antibody absorption test
EIA stands for Enzyme immunoassay.

Interpretations of TPHA test

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