A Dextran Serum Medium for the Demonstration of Incomplete Anti‐a and Anti‐b

SUMMARY A “completing medium” containing dextran, serum and sodium chloride was prepared especially with a view to the agglutination of red cells sensitized with incomplete anti‐A or anti‐B. The “completing medium” was used on a tile at room temperature (20°‐25°C) with an about 5 per cent suspension of the red cells in a saline solution. Readings were taken macroscopically after 10 minutes' slow, intermittent tilting and moving of the tile. The medium agglutinated red cells which were so weakly sensitized with anti‐A that the direct Coombs' test was negative. The medium agglutinated the red cells of two newborn infants with haemolytic disease owing to ABO incompatibility. Coombs' test was negative in both cases. The medium was used in examinations of 500 umbilical cord blood samples. 22 were of Rh‐positive children of Rh‐immunized mothers. Of the rest of the samples, 11 showed agglutination of the red cells in the medium. All 11 children were of group A or B. The mothers were all of group O. Coombs' test was faintly positive in 2 out of the 11 cases. Elution experiments were made in 10 out of the 11. It was demonstrated in all 10 cases that the child's red cells were sensitized with anti‐A or anti‐B. The dextran serum medium is better than a potent antiglobulin serum for the demonstration of A and B sensitization of red cells, but of no use for the demonstration of sensitization with incomplete anti‐Rh.