Specificity of routine parasite serological tests in autoimmune disorders, neoplastic disease, EBV-induced mononucleosis, and HIV infection.

Sera from 120 patients with rheumatological disorders, neoplastic disease, infectious mononucleosis, and HIV infection, and from 30 healthy blood donors were tested for nonspecific reactivity in 13 routinely used parasite serological tests. Responses were detected in 3/30 healthy blood donors (10%) vs 25/120 patients (21%). Of 40 responses in these 28 responders most were weakly reactive, and 25 out of 40 responses were only at borderline level. Response rates were highest in patients with mononucleosis presumably due to heterophile antibodies. Only four patients had responses in at least two different serodiagnostic tests for the same parasitic infection. Response patterns indicative of a possible underlying, concurring, or superimposed parasitic infection, thus, were rare. Especially susceptible to nonspecific reactivity seemed to be immunofluorescent antibody tests for filariasis, schistosomiasis, and amebiasis. In conclusion, compared to healthy controls, false-positive serological responses seem to be more frequent in certain disease groups dependent on the test methods used. Second, the use of more than one serodiagnostic test for the same parasitic disease will substantially facilitate the identification of nonspecific reactivity. Third, for better defining the specificity of parasitological serodiagnosis, more studies should include control sera from patients with nonparasitic diseases that frequently show immunological abnormalities.