The Application of Present Knowledge about the Rh

The purpose of the duplicate test is to avoid the occurrence of an artefact due to traumatisation of the red blood cells, particularly when separating the clot from the wall of the tube. Naturally, care must be taken that the needles and syringes used for the test are perfectly dry. If there is no change in the appearance of the patient's plasma, and the need for blood is urgent, one can then proceed with the transfusion of larger amounts of blood from the same donor. When time permits, however, it is preferable to inject another test dose of 50 cc. of the donor's blood and to draw a third sample of blood after an additional hour. In this way more reliable results can be obtained and the reaction in positive cases is more striking. In positive reactions, one hour after the test injection of 50o cc. of blood, the patient may have a severe chill and rise in temperature, but the clinical symptoms may be quite mild, and occasionally they may be entirely absent. More reliance is to be placed on the appearance of the patient's plasma, which will show a distinct rise in the icteric index as compared with the pre-transfusion sample. The donor's blood used for the biological test should be fresh: if only bank blood is available, no sample more than three days old should be used. The reason for this is that blood stored for periods longer than 7 to 10 days, even though apparently intact when transfused, often breaks down rapidly in the patient's circulation. In this way a positive biological reaction might be obtained even with serologically compatible blood.