(125)IODINE-IOTHALAMATE CLEARANCE IN CHILDREN - A SIMPLE METHOD TO MEASURE GLOMERULAR-FILTRATION

Glomerular filtration rate (GFR) is the most widely used test to evalu ate renal function. Several clearance markers have been used to measur e GFR in adults. In children, however, a simple and reliable method to measure GFR is not available. Renal (125)iodine (I)-iothalamate clear ance, after a single subcutaneous injection, is a simple and accurate test to measure GFR in adults. The validity of unlabelled iothalamate, as a marker for measurement of GFR in children, was reported recently . Unfortunately, the unlabelled iothalamate assay is arduous. We repor t our experience with a single subcutaneous injection of I-125-iothala mate to measure GFR in normal children and those with renal disease. A weight-adjusted dosing regimen was adopted. This regimen resulted in sufficient above-background radioactivity in both blood and urine for reproducible measurement of GFR. Intra-test variability for GFR was no t affected by the degree of renal insufficiency. The test was well tol erated with only 2 patients developing mild headache during the proced ure. Our study showed that renal clearance of I-125-iothalamate is rep roducible, simple, and practical in healthy children and those with mi ld and advanced renal disease.