False Positive Reactions in Treponemal Tests

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Abstract
The authors demonstrated Treponema pallidum immobilizing (TPI) antibodies in goats immunized with normal rabbit testicular homogenates. This finding suggested that false positive TPI tests in human beings might result from reaction of the human serum with rabbit tissue components which could not be separated from the virulent T. pallida utilized in the TPI test. To test this hypothesis 23 serum specimens from patients diagnosed as biologic false positive on the basis of history but giving reactive immobilization results were tested before and after absorption with normal rabbit testicular homogenates. No evidence of removal of antibody by such absorption was obtained. Similar treatment of several sera from patients with syphilis, yaws, and pinta likewise showed no change. Fluorescent treponemal antigen (FTA) studies gave identical results. The fact that absorption of human sera with normal rabbit testicular homogenates did not affect their reactivity in the TPI and FTA tests is in agreement with the known high specificity of these tests.