Plasma volumes of seventeen patients with idiopathic nephrotic syndrome were measured. 125I RIHSA method was used on seven patients and 51Cr-labeled erythrocyte method was used on 10 patients for plasma volume determinations.

51Cr-labeled erythrocyte method gave lower plasma volumes than 125I RIHSA method, and the results expressed as ml/kg body weight gave lower values than the results expressed as ml/m² body surface area. These differences can be explained: 125I RIHSA method specifically measures the plasma space, thus giving more reliable results than 51Cr-labeled erythrocyte method; the differences between results expressed as ml/kg and ml/m² are due to the increased body weight in the edematous state, thus results expressed as ml/kg will be lower than the true values.

In conclusion, it is more accurate to perform plasma volume determination with 125I RIHSA method and to avoid falsely low values the results should be expressed as ml/mg body surface area.