The Clinical Significance of an Increased Nonprotein Nitrogen Content of the Blood
The nonprotein nitrogen of the blood exists in a number of heterogeneous compounds which are chiefly urea, amino acid, uric acid, creatinine, and creatine, and in a group of nitrogenous substances, the composition of which is little known and which are collectively spoken of as the undetermined nitrogen of the blood. Urea is quantitatively the most important component and, because of its ready solubility and diffusibility, it is distributed quite evenly between the cells and the plasma. The amino acids compose the next largest fraction and appear in greater concentration in the cells. Uric acid comprises only a small fraction of the total nonprotein nitrogen and is apparently evenly divided between the corpuscles and the plasma. Creatinine appears in small amounts in the plasma and in larger amounts in the corpuscles, and creatine is entirely confined to the cells. The undetermined nitrogen factor which comprises approximately one-third of the total nonprotein nitrogen in the blood is largely confined to the cells.
The total nonprotein nitrogen of normal whole blood ranges between 28 and 42 mg. per 100 cc. with an average of 32 mg. The urea nitrogen varies between 9 and 16 mg. per 100 cc. with an average of 12 mg. with urea values between 20 and 35 mg. The amino acid nitrogen varies between 6 and 8 mg. per 100 cc. with an average of 6 mg., and the undetermined nitrogen comprises between 10 and 18 mg. with an average of 14 mg. Uric acid determinations on normal. . .