Blood Grouping 413 



in that the cells and antisera are shaken in the test tube and spun 

 down with the aid of a centrifuge. Clumping of the resuspended 

 cells after spinning down can be detected both macroscopically 

 and microscopically, and some of the weaker reactors will be de- 

 tected more readily than with the slide method. 



CROSS-MATCHING 



Having determined the blood type, another important operation 

 before administering blood to a patient is to conduct a cross- 

 match of donor's and recipient's bloods. This precaution will 

 detect bloods that are incompatible for reasons other than dif- 

 ferences in O-A-B types, and cross-matching serves as a double 

 check on the accuracy of the original typing of the blood specimen. 



Best results are obtained in cross-matching when undiluted 

 samples of blood are employed. A sample of the donor's cells is 

 mixed with the recipient's serum (the so-called major side of a 

 cross-match), and a sample of the recipient's cells is mixed with 

 some of the donor's serum (the minor side). To be compatible, 

 there must be no agglutination on the major side, and only minor 

 clumping may be permitted on the minor side. It is the injected 

 blood cells that are important in blood transfusions; any clumping 

 by the recipient's serum will lead to severe consequences, and 

 possibly death of the patient. It is not a safe practice to repeatedly 

 administer blood from the same donor to a given patient without 

 cross-matching the bloods each time. Serological changes may 

 have taken place since a previous transfusion, and severe reactions 

 may result. 



THE Rh FACTOR 



In 1940 Landsteiner and Wiener reported that when the red 

 cells of Macacus rhesus monkeys were introduced into rabbits and 

 guinea pigs, antibodies were evoked which caused clumping not 

 only of monkey red cells, but also of the red cells of about 85% 

 of human beings. The antigenic factor in human erythrocytes 

 responsible for this reaction was named Rh (for rhesus). This 

 relatively simple concept of Rh-positive and Rh-negative blood 



