Question

1.The TP PA test uses sensitized and un-sensitized particles.  What is the difference between these two reagents?  Be specific.

2.This test gives results comparable to the FTA ABS.  In addition to the fact that TP PA is an agglutination test and FTA ABS is a ligand assay there is another significant difference.  What is the difference and why do you think this step is different?

3.Serum must be diluted prior to testing, what is the final dilution of the specimen?

4.Why are un-sensitized particles added to diluted serum?

5.What does a non-reactive specimen look like?

Answer 1

1. sensitised particles :lyophilized preparation of colored gelatin particles coated with T.pallidum

unsensitized particles : lyophilized preparations of colore gelatin particles not coated with T. pallidum

2. FTA ABS test uses dilution that inactivated patient serum that is incubated with a mixture of sorbent and non-pathogenic treponemes. This technique allows the removal of any cross reactivity with treponemes other than T. pallidum. both test are sensitive but the FTA-ABS is sensitive and highly specific.
TP-PA test uses colored gel particles with a treponomel antigens which makes it sensistive to primary syphillis but is a not specific

3.final dilution : 1:80

4. The unsensitized particles are a negative control. When mixed with patient sample no agglutination should occur

5. non reactive specimen : no syphilis or Probable false-positive screening test