The Determination of Blood Urea

Most of the methods for the determination of urea in blood involve the use of the enzyme urease to hydrolyze the urea, since this reaction is specific. However, instead of crystalline urease (l), crude jack bean meal extracts are used. These extracts have been found to contain other enzymes besides urease, termed “ammonia-producing” enzymes, and their substrates, which may produce large quantities of ammonia when incubated with blood. Although the ammonia-producing enzymes are inactive at the pH value of jack bean meal extract, when the extract is added to blood the resulting digest is sufficiently alkaline to activate these enzymes. In order to obtain correct values for blood urea, it is therefore necessary to determine the value for the ammonia formed by the extracts when they are incubated, in the absence of blood, under the same conditions. Previous values published for blood urea have not been corrected for the ammonia produced by the meal enzymes. Since it has been found that the usual method for the determination of urea involves a complicated procedure to correct the error produced by the extract, a new method for the determination of blood urea, with jack bean meal extracts, has been devised wherein the ammonia-producing enzymes are inactive. The use of this new method in the determination of urea in human blood has been investigated. Urease powders prepared from jack bean meal have also been investigated. A commercial preparation of urease powder has been found which produces ammonia spontaneously and yields erroneous values when used in the determination of blood urea. Laboratory preparations of urease powders contain an ammonia-