Glomerular Filtration Rate in Patients With Severe and Very Severe Renal Insufficiency

Clearance studies in patients with markedly reduced renal function can be performed with satisfactory accuracy without catheterization of the bladder. A reliable infusion technique, careful instruction and supervision during the study, together with clearance periods of adequate length, are necessary. Endogenous creatinine clearance does not provide a reliable expression for glomerular filtration in patients with renal insufficiency and in patients with the nephrotic syndrome, because renal function is consistently overestimated. This overestimation is approximately 25 to 50% in patients with an inulin clearance less than 25 ml/min. 125 iothalamate clearance in the same series of patients provided an exact measure of glomerular filtration rate, as the mean ratio c Io/ c In was 0.97.