Elimination of Rheumatoid Factor in the Latex Test for Cryptococcosis

Abstract

False-positive agglutination by rheumatoid factor (RF) of specifically sensitized latex particles in the slide latex-agglutination (SLA) test for cryptococcosis is eliminated (one apparent exception is noted) by prior addition to the test serum of 0.003 M dithiothreitol (DTT). The IgM responsible for nonspecific clumping is inactivated by reduction, while cryptococcal polysaccharide antigen is unaffected. In no case of proven cryptococcosis was the SLA reaction eliminated by 0.003 M DTT. By revealing alterations in titer, however, the meunod detects coexisting rheumatoid arthritis and cryptococcosis. Treatment of cryptococcal SLA-positive sera with DTT should obviate the need for the RF test control currently contained in commercial kits.