The RhoVariant - Du

A series of experiments to assess the influence of several variables in a direct tube test for the Du factor and a set of conditions that give optimal results are reported. The most important of the latter is the maintenance of a high protein content. The reagent should have a 25 per cent albumin concentration; its titer should approximate 1/128 and it should be specific, particularly for the various types of weak “low grade” Du. The applicator stick method for transferring the unknown cells from clotted or whole blood reduces the dilution of reagent that occurs when one drop of a light cell suspension in serum is used. Centrifugation at the relatively high R.C.F. of 1,200 is the other salient point of the test; following this, the test is completed by the addition of one drop of saline and a direct reading. A scheme is proposed for the application of the direct Du tube test, in conjunction with an anti-CDE reagent, to typing donor bloods. It permits, in one direct test, the division of D negative bloods into a group consisting exclusively of type ccddee and a small group which includes all combinations of D negative bloods having factors C, Du and E. The phenotypes of the latter bloods can then be readily established in conjunction with routine methods and the direct Du tube test. Using the direct Du tube and the indirect antiglobulin methods in parallel tests of 28 Du positive bloods, the former was the equal in accuracy and sensitivity of the antiglobulin test. The conditions which lead to false positive reaction with the tube test also gave false positive reactions with the antiglobulin test. With cells of very “low grade” type CcDuee and/or ccDuEe, false negative reactions were encountered with both methods. However, 13 examples of low grade type ccDuee bloods were studied; all gave relatively strong positive reactions with both methods. These studies indicate that the direct Du tube method is deserving of trial under the conditions of a routine blood typing program, particularly as experienced in the collection of large numbers of donor bloods. They also suggest that the test will be found the equal of the indirect antiglobulin test both in sensitivity and accuracy at a significant reduction in technician time and reagents.