Emergency Methods for Rhesus Group Determination.

The most reliable method for Rhesus group determination is probably the standard tube method (Landsteiner and Wiener, 1941; Boorman, Dodd, and Mollison, 1942; Taylor, 1943). This technique has only one serious disadvantage: it may take as long as two hours to perform, although occasional high-avidity anti-D sera will give clearcut results in 30 minutes or even less. For emergency Rhesus typing a considerably quicker procedure is desirable. Rapid methods which have been described include the Chown capillary tube test (Chown, 1944; Chown and Lewis, 1946) and the Diamond slide test (Diamond and Abelson, 1945). Mollison, Mourant, and Race have recommended centrifuging after ten minutes' incubation as a means of accelerating agglutination in the tube method. In pre-transfusion Rhesus grouping in this laboratory, it has been the practice for some time to use the Chown method. The results were checked by the tube method carried out by a different observer working in a separate room. Where both tests were in agreement, it was assumed that the correct result had been found: whenever discrepancies occurred, investigations were repeated until no reasonable doubt remained. After several hundred parallel observations had been made in this way, it became clear that the Chown test, at any rate with the technique in use, was not altogether satisfactory: both false positive and false negative results were occasionally encountered. We therefore decided to carry out a number of experiments to try to discover the reasons for incorrect results in the Chown test, and to determine as far as possible the optimum conditions for the test. At the same time a trial of the tube centrifuging method was made in parallel with the other two techniques. We aim in this paper to compare the reliability of three methods for Rhesus group determination as used in a routine laboratory; to draw attention to some sources of error in the Chown test ; and to describe the conditions in which satisfactory results can be obtained with the tube centrifuging method.