Studies on the Treponemal Immobilization Test. III. Use of the TPI as a Verification Test in Suspected Latent Syphilis

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Abstract
Wilkinson and Sequeira studied the Treponemal Immobilization Test (TPI) as a verification test in suspected latent syphilis. Immobilizing antibody was demonstrated in all but one of 136 patients in whom the diagnosis of latent syphilis was corroborated by other evidence than the STS results alone. In view of the specificity of the test, its great sensitivity, and its ability to give clear-cut results, it is thought to be eminently suitable as a verification test in patients with suspected latent syphilis. In an untreated patient where the only presumptive evidence of syphilis rests on positive STS results, it is considered that a negative TPI test, confirmed on a 2nd specimen of serum, is good evidence that the STS results are non-specific in nature. The TPI was found to be negative in 11.5% of 200 untreated patients coming to venereal disease clinics with suspected latent syphilis, and in 4.4% of 248 such patients who had been diagnosed and treated for latent syphilis in the past. 35% of problem sera from blood donors, and 27.5% of problem antenatal sera from patients found to be STS-positive on routine testing gave negative TPI tests. In an unselected group of antenatal sera about 1/5 of those giving positive STS were TPI-negative. Of 149 patients with diseases other than syphilis who had been found STS-positive, on routine testing, 29% gave negative TPI tests.