[A new analytical method for simultaneous measurement of iothalamate and iohexol]

Glomerular filtration rate (GFR) is believed to be the overall index of renal function, and the renal clearance of inulin (Cin) obtained during constant intravenous infusion has long been accepted as the gold standard of GFR measurement. Because of a number of technical difficulties inherent in the assay of inulin concentration in urine and plasma, its utility in clinical practice is limited. Iothalamate, urographic contrast medium, which behaves and is excreted in a fashion similar to inulin, has been accepted as a good filtration marker. We examined whether GFR could be estimated by ionic contrast media, "iothalamate" and non-ionic contrast media, "iohexol", when the high-performance liquid chromatography (HPLC) system was used as the analytic method. In our HPLC system, iothalamate and iohexol could be simultaneously determined. The assay results gave linearity within the wide range of concentrations tested. In seventeen subjects, the renal clearances of creatinine, iothalamate, and iohexol (Ccr, Ciot, and Cioh) were compared with that of inulin. The slopes with zero intercept of Ccr vs Cin, Ciot vs Cin, and Cioh vs Cin were 1.24 +/- 0.02, 1.06 +/- 0.02, and 0.83 +/- 0.02, respectively. In conclusion, an excellent correlation of renal clearance of iothalamate with that of inulin was obtained in patients with a wide range of renal function and normal volunteers. This justifies the use of the single injection of iothalamate and HPLC system as the analytic method in the measurement of GFR.