Improved dextran sulfate-calcium chloride method for the removal of nonspecific inhibitors with modifications for nonspecific agglutinin removal in the rubella hemagglutination inhibition test.

The dextran sulfate precipitation method for removal of nonspecific inhibitors from sera to be tested in the rubella hemagglutination-inhibition test was modified by shortening the dextran sulfate-serum mixture incubation period from 2 hr to 30 min. A comparative study using both treatment times showed no significant difference in rubella antibody titers. Reducing the treatment time even further also gave comparable results, indicating the select 30-min incubation period is not marginal for undertreatment. It was shown that 41.5% of the 159 serums tested had nonspecific agglutinins at levels from 1:8 to as high as 1:64. In each specimen, all demonstrable nonspecific agglutinin was removed by adsorption with 10%, 0- to 2-day-old chick red blood cells rather than the usually recommended 50% adult chicken erythrocytes.