Measurement of glomerular filtration rate utilizing a single subcutaneous injection of 125I-iothalamate

The measurement of glomerular filtration rate (GFR) is an important index in the evaluation and follow-up of patients with renal disease and transplant recipients. Unfortunately, its clinical usefulness was limited for many years because of the difficulties associated with the measurement of inulin clearance. Marked simplification in the measurement of GFR occurred as a result of the introduction of radioactively-labeled iothalamate, a substance reported to be handled by the kidney in an identical manner as inulin [1].1 Sigman, Elwood and Knox [3], as well as others [4–7], clearly demonstrated that the clearance of isotopically labeled iothalamate, administered by continuous infusion, was identical to that of inulin over a wide range of filtration rates. Subsequently, the measurement of GFR was simplified further by the utilization of a single intravenous injection of labeled iothalainate [8–10]. Unfortunately, the results obtained with the single intravenous injection have not been uniformly in agreement with the simultaneously measured inulin clearance. Therefore, a new technique for the administration of iothalamate has been introduced.