837 



The simplest way to determine to what group a given blood belongs 

 is to test its cells against the sera of groups 2 and 3. The reason why 

 one may determine the group by these two agglutination tests is because, 

 as will be seen by reference to Table III, there are but four possible com- 

 binations of positive and negative reactions of unknown cells with known 

 sera of groups 2 and 3. These four different combinations, one for each 

 of the four groups, allow identification of unknown cells by the presence 

 or absence of their agglutination by groups 2 and 3 sera. It serves as an 

 excellent control if when the group is determined a test is made between 

 the unknown cells and group 4 serum, in addition to groups 2 and 3 sera. 



While it is always advisable to choose a donor who belongs to the 

 same blood group as that of the patient, this is by no means always neces- 

 sary. This is because, owing to certain protective mechanisms associated 

 with a preponderating blood whose cells can be agglutinated by other 

 sera, it is possible to give plasma which can in vitro agglutinate and 

 hemolyze the cells of such blood. However, in the body, the blood of 

 the recipient will prevent agglutination or hemolysis of its cells by the 

 donor's plasma if the transfusion is given under suitable conditions and in 

 at least the usual amounts. One can never give, without serious risks, 

 red cells that can be agglutinated by the patient's plasma, which is under 

 usual conditions the preponderating plasma following transfusion. Con- 

 sequently, a group 4 donor may be regarded as a universal donor, since 

 his cells cannot be agglutinated by any plasma, and a member of group 1 

 can be regarded as a universal recipient since his plasma can agglutinate 

 the cells of no other group. It is, as stated, desirable to transfuse blood 

 within the same group, yet as a practical measure it has been demonstrated 

 repeatedly that blood of group 4 can be utilized for transfusion in any 

 one of the four groups. 



The practical advantage of regarding a member of group 4 as a uni- 

 versal donor is, of course, obvious. It merely requires the testing of a 

 donor and does not require the testing of a patient. This enables one to 

 have a supply of group 4 donors on hand for possible emergency trans- 

 fusions. With the presence of a combination of a great reduction of 

 blood volume, a marked reduction of red cells, an anticipated transfusion 

 of a large amount of blood, and a strong iso-hemolysin in the donor's 

 blood, it is unwise to transfuse from a group 4 donor into a recipient of 

 another group. Clinical experience justifies this exception to the rule of 

 the use of group 4 individuals as universal donors, when it is difficult to 

 obtain a donor of the same group as that of the patient. It is, however, 

 more desirable under any circumstances to use a group 4 donor for an 

 individual of another group than one thought to belong to the same 

 group as the patient, but whose group designation is not clear cut. This 

 is particularly true when dealing with groups 1 and 3 patients whose iso- 

 agglutinins and red cell receptors are apt to be of a weaker nature than 



