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.

Results of comparative tests using trypsin-modified human type 0 erythrocytes and cells from newly hatched chickens with three standard serum treatment methods for rubella hemagglutination-inhibition techniques are reported. The kaolin, heparin-manganous chloride and dextran sulfate-calcium chloride methods could all be used with both cell types. Reproducibility with heparin-manganous chloride and dextran sulfate-calcium chloride was excellent with both cell types. Both methods gave generally higher antibody titers than the kaolin procedure. However, the use of human cells resulted in a more sensitive system than chicken cells with all serum treatment methods.

Results of comparative tests using trypsin-modified human type O erythrocytes and cells from newly hatched chickens with three standard serum treatment methods for rubella hemagglutination-inhibition techniques are reported. The kaolin, heparin-manganous chloride and dextran sulfate-calcium chloride methods could all be used with both cell types. Reproducibility with heparin-manganous chloride and dextran sulfate-calcium chloride was excellent with both cell types. Both methods gave generally higher antibody titers than the kaolin procedure. However, the use of human cells resulted in a more sensitive system than chicken cells with all serum treatment methods.

A method of treating human erythrocytes with trypsin has been modified and found to be an efficient and practical indicator system for the rubella hemagglutination-inhibition test. Both the trypsin-treated human cells and the widely used, newborn chicken erythrocytes were used in comparative testing of 464 selected diagnostic rubella serums. Results with each cell system were essentially the same. The trypsin treatment procedure has been found to be relatively simple, and with our limited testing has not presented any problems with reproducibility. Other advantages include the ready availability of human cells, greater intralaboratory standardization of the test by using the same donors over a long period of time, and elimination of adsorption of test sera with red blood cells.