DETERMINATION OF EXTRACELLULAR FLUID VOLUME IN UREMIC PATIENTS BY ORAL-ADMINISTRATION OF RADIOSULFATE

Determinations of extracellular fluid volume (ECF) are needed both for understanding and management of problems in patients with hypertension and chronic renal disease. Because of difficulties with i.v. radioisotope markers, accuracy of oral radiosulfate (100 μCi) was assessed in four groups of subjects. In all, radiosulfate space correlated with expected value for weight, but equilibration time and decay rate of plasma levels was significantly more rapid in normal volunteers than it was in chronic renal failure (94 ± 8 vs. 161 ± 16 min and 14.6 ± 0.9 vs. 0.5 ± 0.1% hr, respectively; P<0.001). Repeated determinations in hypertensive patients maintained on constant sodium intake varied by 2.6 ± 1.1%. Moreover, oral radiosulfate was sensitive enough to detect changes induced by either hemofiltration (14 patients) or saline infusion (4 patients); variations in body weight and radiosulfate space correlated closely (r=0.99) with a slope of 1.03. Thus, this method can provide reproducible and accurate measure of ECF changes in subjects with either normal or impaired renal function. Clinical value was demonstrated by finding fluid overload (radiosulfate space, 25 ± 1.1% of body wt vs. 18.9 ± 0.7% for normal) in absence of clinical signs of fluid retention in 11 out of 18 patients on regular hemodialysis.