Measurement of the Extracellular Fluid Volume by Thiosulfate. II. The relation between the apparent volume of distribution of thiosulfate and the volume of distribution of inulin

Summary. The volumes of distribution of inulin and thiosulfate were compared in 24 healthy adults and 14 patients. The apparent volume of distribution of thiosulfate (VTS) was found to be of the same magnitude as that of inulin (VIN), the mean VTS: VIN ratio being 1.03 ± 0.02. The discrepancies between apparent VTS and VIN were rather large, the VTS: VIN ratio ranging between 0.70 and 1.33 with a coefficient of variation of 13.9 per cent. These discrepancies could be in part accounted for by the variations of the rate of disappearance of thiosulfate from plasma. An equation is presented for the calculation of the volume of distribution of inulin from the apparent volume of distribution of thiosulfate.