A simplified method of performing the Treponema pallidum immobilization test.

The standard TPI test is a complicated technique that can be performed only by highly qualified staff in well-equipped laboratories. This has greatly restricted its application. The author describes a simplified method that does not require complicated apparatus or the use of a gas mixture. The test is performed in diluting pipettes of the type used in making white blood cell counts. The serum to be tested and treponemal suspension containing active complement are taken up successively into the pipette, which is then closed with a rubber ring, shaken and placed in the incubator. A parallel series of control pipettes with inactivated complement is also set up. After incubation, counts of motile and non-motile treponemes are made in the usual way. Comparative studies have shown that the results obtained with this simplified test are comparable in accuracy to those of the standard method. The medium used by the author for preparing the treponemal suspension is also very simple in composition. The technique can therefore be performed in any laboratory that has qualified staff and facilities for keeping rabbits.