Evaluation of a new rapid plasma reagin card test as a screening test for syphilis

This study evaluates the American Dade (Biokit Laboratories) rapid plasma reagin (Dade RPR) card test, currently used in Spain for the diagnosis of syphilis, which has been recently released to the U.S. market. Used as a basis for comparison with the Dade card test were the 18-mm standard rapid plasma reagin (standard RPR) card test and the Venereal Disease Research Laboratory (VDRL) slide test, using both fresh sera obtained from 505 individuals and paired serum-plasma specimens from 174 individuals. Results obtained proved the Dade RPR card test with serum to be very similar to the standard RPR card test; sensitivity was 92.3% and specificity was approximately 99% for both RPR card tests. Although the sensitivity of the VDRL slide test was lower at 88.5%, its specificity was also approximately 99%. Quantitatively, the agreement +/- 1 dilution between the two card tests was 93.6%. Agreement +/- 1 dilution between the Dade RPR card test and the VDRL slide test was 46.5% for sera, comparable to the standard RPR-VDRL agreement of 50%. In the limited evaluation of the RPR card tests with plasma, the specificity was 99.4% and the sensitivity was 100% for both tests. Quantitative agreement +/- 1 dilution between plasma and serum pairs was 100% for the Dade RPR card test. Our results showed that the Dade RPR card test is as sensitive and as specific as the standard RPR card test. Therefore, it was concluded that one card test has no particular advantage over the other.