Ultrasound pre-treatment can extend immunoagglutination test sensitivity while avoiding the prozone phenomenon

The lower sensitivity limit of slide-based latex particle immunoagglutinati on assays can be significantly improved by applying an ultrasonic standing wave field to reactants held in a capillary tube. The method is most effect ive when used with diluted test latex reagent, Agglutination-inhibition (th e prozone phenomenon) caused by increased antigen loading per diluted micro particle, was examined here. The analyte concentration at which the prozone effect occurred in a P-galactosidase agglutination test was four-fold high er at the optimal latex dilution (1/8 of neat suspension) for ultrasound, t han was the case for the conventional undiluted latex test-card procedure. Ultrasound increased the detectable range of antigen by 128-fold. Commercia l kits (for C-reactive protein and bacterial antigen) showed no increase in prozone occurrence using diluted latex in conjunction with ultrasound. Ult rasound, therefore, in addition to reducing the lower limit of antigen dete ction, may reduce false negative results due to the prozone effect.