Serologic testing for Trypanosoma cruzi: Comparison of radioimmunoprecipitation assay with commercially available indirect immunofluorescence assay, indirect hemagglutination assay, and enzyme-linked immunosorbent assay kits

The radioimmunoprecipitation assay (RIPA) has been used as a confirmatory t est in several ongoing and published studies of Trypanosoma cruzi in blood donors in the United States. Despite its use as a confirmatory test, few st udies are available comparing RIPA to commercially available serologic test methods. Thus, we compared RIPA with two indirect hemagglutination assays (Biolab Diagnostics SA, Sao Paulo, Brazil; Hemagen Diagnostics, Inc., Walth am, Mass.) and four different enzyme-linked immunosorbent assays (Abbott La boratories, Abbott Park, Ill.; Embrabio, Sao Paulo, Brazil; Organon Teknika , Sao Paulo, Brazil; and Gull Laboratories, Salt Lake City, Utah) using a p anel of 220 serum specimens from Brazilian blood donors with a range of T. cruzi antibody titers as determined by indirect immunofluorescence assay (I FA). A titer of 1:20 was used as the baseline for seropositivity. All IFA-n egative serum specimens (n = 19) were nonreactive on all tests. At a titer of 1:20 (n = 9), reactivity rates varied considerably among the tests, with only the RIPA and the Organon and Gull assays identifying reactive specime ns. For specimens at a 1:40 titer (n = 35), most assays identified at least 32 of 35 (91%) specimens as reactive, but the Biolab assay only identified 24 (69%). At higher titers (1:80, n = 56; 1:160, n = 101) the assays were comparable, with the exception of the Biolab assay, demonstrating rates of agreement with IFA of greater than or equal to 98%. Overall, when compared with several other test formats, RIPA demonstrated equivalent or superior r ates of agreement with IFA-positive specimens across all titers examined. I n particular, at titers of >1:40, the RTPA compared favorably with other te st methods currently in use, supporting Its application as a confirmatory t est, particularly in a research setting.