Effect of adverse storage conditions of antigen reagent on performance of the rapid plasma reagin test.

The aim of this study was to evaluate the performance of rapid plasma reagin (RPR) testing using expired and adversely stored antigen reagent. The sensitivity of RPR using antigen stored at 36 degrees C was compared at 3-monthly intervals with RPR using fresh antigen on 116 sera reactive by RPR and by Treponema pallidum particle agglutination (TPPA). After multiple phases of freezing and thawing, 8.3% of initial RPR reactive sera seroreverted. After storage at 36 degrees C for one year and 24 weeks after expiration the overall sensitivity of the adversely stored antigen was 93.8% compared with fresh antigen; the sensitivity was 100% for sera with RPR titres > or = 1:4 and 85.4% for sera with RPR titres of 1:1 and 1:2. The high stability of the reagent may increase the feasibility of the RPR test for use in poorly-equipped healthcare centres in developing countries.