Uric acid and endogenous creatinine clearance studies in normal pregnancy and toxemias of pregnancy

Abstract

Definite and characteristic changes in renal function as measured by endogenous creatinine and uric acid clearances can be demonstrated in pregnant women with pre-eclampsia and in those with acute toxemia superimposed upon chronic hypertension, those with essential hypertension, and those with unclassified “toxemia,” when compared with normal pregnant women. In normal women both the creatinine and uric acid clearances were higher prior to the thirty-second week of pregnancy when glomerular filtration reaches a maximum than they were during the last 8 weeks of the gestation period. In most instances the figures were higher than those considered to be normal for nonpregnant women, irrespective of the period of gestation at the time the test was made. It is necessary to recognize this variation particularly in setting up a standard for the comparison of renal function in abnormal conditions.The normal fall in the clearances as pregnancy advanced was not observed in patients with essential hypertension unless it was complicated by a superimposed acute process, in which event both the uric acid and the creatinine clearances were reduced simultaneously. The changes in the latter patients were almost identical with those observed in women with preeclampsia and on the basis of the clearance studies alone it was impossible to differentiate one from the other. The reduction in renal function tended to be greater the more severe the toxemia but this relationship did not always hold true because there was considerable overlapping of results.The clearance studies of both uric acid and creatinine provided a far more accurate evaluation of the exeretion of the materials than did the blood levels. Abnormally high blood creatinine levels were seldom observed and those of uric acid often were normal even though the clearance was reduced.Because the changes in the creatinine and the uric acid clearances follow each other so consistently in normal as well as in abnormal patients, it seems likely that the low clearance of uric acid in pre-eclampsia, which often is attributed to a selective increased tubular reabsorption, actually represents a decreased glomerular filtration of the material.Single clearance studies are of little value in either diagnosis or prognosis but relative changes in the creatinine and uric acid excretion usually can be observed as the severity of toxemia progresses and may be helpful, when considered in relation to the clinical signs, in determining treatment. A single uric acid or creatinine clearance study will not often indicate those who will develop pre-eclampsia, but a progressive fall which is greater than the normal and which antedates positive clinical signs can be detected with serial tests and may be useful in prognosticating the development of pre-eclampsia.