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 reagi n (RPR) testing using expired and adversely stored antigen reagent. The sen sitivity of RPR using antigen stored at 36 degreesC was compared at 3-month ly intervals with RPR using fresh antigen on 116 sera reactive by RPR and b y Treponema pallidum particle agglutination (TPPA). After multiple phases o f freezing and thawing, 8.3% of initial RPR reactive sera seroreverted. Aft er storage at 36 degreesC for one year and 24 weeks after expiration the ov erall sensitivity of the adversely stored antigen was 93.8% compared with f resh antigen; the sensitivity was 100% for sera with RPR titres greater tha n or equal to1:4 and 85.4% for sera with RPR titres of 1:1 and 1:2. The hig h stability of the reagent may increase the feasibility of the RPR test for use in poorly-equipped healthcare centres in developing countries.