EDTA-treated plasma in the rapid plasma reagin card test and the toluidine red unheated serum test for serodiagnosis of syphilis

Abstract

Both the rapid plasma reagin (RPR) 18-mm circle card test and the toluidine red unheated serum test (TRUST) were designed to be more rapid than the Venereal Disease Research Laboratory slide test for the serodiagnosis of syphilis. The RPR card test, although originally designed as the teardrop card test for use with plasma, has received recognition from the Centers for Disease Control as a standard test for syphilis for use with serum samples only. In this study, 132 EDTA plasma-serum pairs were tested in both the RPR card test and TRUST immediately after the blood was drawn and the serum or plasma was separated from the cellular constituents of the blood. The plasma samples were further tested at 24-h intervals of storage at 25 and 4 degrees C for 72 h. Special attention was paid to any increase in roughness in nonreactive specimens. The greatest increase in roughness (16.7%) was seen with the TRUST after 72 h at 25 degrees C. An additional 174 plasma-serum pairs were tested after 18 h of storage at 25 degrees C. Comparisons of the results of the 306 serum specimens with their corresponding plasma pairs gave 99.0% qualitative agreement for both tests. Quantitative agreement +/- 1 dilution between serum-plasma pairs tested within 18 h was 92.1% (35 of 38) for the RPR card test and 94.1% (32 of 34) for the TRUST. Our results with plasma from blood drawn with EDTA as the anticoagulant were comparable with results with serum specimens for both tests when plasma specimens were tested within 18 to 24 h.