Improved detection of bacterial antigens by latex agglutination after rapid extraction from body fluids

Nonspecific agglutination of antibody-coated latex particles, unrelated to the presence of specific bacterial antigens, is a major difficulty with commercial latex particle agglutination tests. Rheumatoid and other factors are known to interfere with latex tests. We studied the use of six chelating, reducing, and anticoagulatory reagents in a rapid extraction of antigen procedure to free heat-stable antigens of Haemophilus influenzae type b and group B streptococcus which had been added to human sera. We also screened sera for the incidence of nonspecific agglutination from the three following groups: 123 patients with positive serology tests, 112 hospitalized patients, and 87 blood donors. The rapid extraction of antigen procedure involved a 1:4 dilution of the sera with each of the six reagents, incubation at 100 degrees C for 3 min, and centrifugation at 13,000 X g for 5 min. Two commercial latex kits were tested (Bactigen and Wellcogen). Nonspecific agglutination was entirely eliminated by each of the six extraction reagents. Sera from 52% of the patients with positive serology tests, 29% of the hospitalized patients, and 28% of the blood donors showed nonspecific agglutination with Bactigen before extraction. Nonspecific agglutination was eliminated in all but one sample after the rapid extraction of antigen procedure. This simple, rapid extraction procedure eliminated nonspecific reactions in cerebrospinal fluids and amniotic fluids and reduced this problem in urines and sera with each commercial kit used on clinical specimens.