Abstract
The importance of using only serum of high titer in determining human blood groups has been emphasized by Coca. 1 The risk involved in accepting a serum merely on correctness of type without attention to titer is shown by Coca's findings on examination of 16 sera in actual use in New York City, none of them coming up to his Grade I and only 4 to his Grade II.
Coca's standard for Grade I requires that a 1-4 suspension of cells be agglutinated macroscopically in one minute by a 1-4 dilution of the serum; by a 1-2 dilution for Grade II. Group “B” serum of acceptable titer (Grade II or better) is fairly common among persons of that relatively rare group. This cannot be said of Group “A”, however. In either group a high-titer serum is the exception. It would seem, therefore, that a method for raising a low-titer serum to acceptable grade would be useful, particularly in the case of the usually low titer Group “A” serum.
Our method consists in repeatedly freezing and thawing a tube of the serum in an ice and salt mixture and recovering the lower portion of the contents of the tube after the last thawing. An indication of what takes place may be seen if, between freezings, the tube is gently tilted back and forth, whereupon a movement of heavy oily-looking streaks occurs between a darker colored lower portion and a lighter colored upper portion. Ultimately the lower portion becomes deeply colored and the upper portion colorless and the lower portion will be found to have a higher agglutinin titer than the whole serum had originally.
By this method we have obtained from a serum which originally did not agglutinate macroscopically in 1-4 dilution a product which agglutinated in 1-16 dilution.
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