The Measurement of Glomerular Filtration Rate and Effective Renal Plasma Flow in Man by Iothalamate 125 I and Iodopyracet 131 I

Abstract

In 21 patients, 90 simultaneous renal clearances of inulin and sodium iothalamate ¹²⁵I, and para-amino-hippuric acid (PAH) and iodopyracet ¹³¹I were determined by a constant infusion technique. The activities of iothalamate ¹²⁵I and iodopyracet ¹³¹I were determined simultaneously in a dual-channel scintillation counter. The concentrations of inulin and PAH were determined by standard chemical techniques. The ratio of iothalamate ¹²⁵I to inulin clearance ranged from 0.93 to 1.09 with a mean of 1.00. The ratio of iodopyracet ¹³¹I to PAH clearance varied from 0.86 to 1.04 with a mean of 0.96. The chemical determination of PAH and inulin required approximately 8 hours of technician time as compared with 30 minutes by the radioactive technique. The determination of the renal clearances of iothalamate ¹²⁵I and iodopyracet ¹³¹I is an accurate and time-saving technique for the measurement of glomerular filtration rate and effective renal plasma flow.