A New Method for the Determination of Urea in Blood

In a recent number of this Journal,’ a new method for the estimat,ion of urea in urine was described. This method consists in the conversion of the urea into ammonium carbonate by means of the urease of the soy bean, and an estimation of the alkalinity before and after the conversion by means of standard acid and methyl orange. The procedure is not directly applicable to the est,imation of urea in blood serum owing to the large quantity of proteins and small amount of urea present. Hpwever, by a conversion of the urea into ammonium carbonate with the use of the enzyme, and a subsequent removal of the ammonia by means of an air current as suggested by Folin,2 satisfactory results can be obtained without a preliminary removal of the proteins, as is necessary in other methods for the determination of urea in blood. Procedure. The blood is drawn in the usual manner and allowed to stand on ice until clotting is complete. As shown below the urea content of the serum does not change after standing even for three or four days; the blood can, therefore, be kept on ice over night, if desired. Two equal portions of the serum are measured into ordinary test tubes, 1 cc. of the soy bean extract3 added to one tube, and