The urea content of the blood

Abstract

Although the retention of urea nitrogen in the blood is now generally regarded as a reliable diagnostic sign of faulty kidney function, there still remains a disturbing degree of confusion as to what should be considered the normal and what a pathological urea content of the blood. Repeated observations of Folin and Denis, and those of our own laboratory, seem to prove conclusively that in normal adults the concentration of urea nitrogen is from 12 to 15 mg. per 100 c.c. of blood. A study of the records of routine blood analyses of hospital patients, on the other hand, shows that many individuals without symptoms of kidney lesion have a urea nitrogen of more than 15 mg. per 100 c.c. of blood. Of a series of 244 cases, extending over a period of 5 months, 206, or 84 per cent., had a urea nitrogen concentration of not more than 20 mg. per 100 c.c. Of these 206 cases, 83, or 40 per cent., showed some indications of kidney lesion, while of the remaining 38 cases in which the urea nitrogen was more than 20 mg., 29, or 76 per cent., showed other renal symptoms. Throughout the series the higher blood urea was closely paralleled by the greater degree of kidney lesion, as indicated by presence of casts or albumin in the urine, high blood pressure, high blood sugar and creatinine or low phthalein output. From these observations we conclude that 20 mg. per 100 c.c. may be taken as upper normal limit of urea nitrogen in the blood of hospital patients.