Control of the antigen-antibody ratio in antibody detection/compatibility tests

An evaluation was made of the variation and importance of dropper volume delivery on pretransfusion testing in ten hospital transfusion services which annually perform a combined total of 225,000 compatibility tests on the serum of approximately 70,000 patients. The pretransfusion testing by these institutions typifies practices throughout the United States in that serum and red blood cells are used with little awareness of actual volumes used and the resultant proportion of one reactant to the other. Tests of the hospitals' dropper pipettes showed a range of serum delivery per test of 0.0465 to 0.1155 ml. Commercial reagent red blood cell vial droppers delivered (according to cell concentration) from 0.00166 to 0.00294 ml packed red blood cells (pcv). From these findings, it could be shown that the serum to cell ratio in the tests done in two transfusion services was as low as 19 to 1 and that the highest ratio of 70 to 1 was used in only one institution. In none was the serum-cell ratio the optimum of 80 to 1.