ASSESSMENT OF GLOMERULAR-FILTRATION RATE UTILIZING SUBCUTANEOUSLY INJECTED CR-51-EDTA

1. Cr-51-EDTA injected with lidocaine and epinephrine, as a subcutaneous button, is slowly absorbed, and a plasma level that is relatively stable can be maintained for a time sufficient to permit measurement of the renal clearance of EDTA, which is a measure of glomerular filtration rate (GFR). We studied this procedure in 32 normal volunteers and 24 patients with different glomerulopathies, comparing EDTA and creatinine clearances. In 20 patients these measurements were also compared with inulin clearance. 2. Creatinine clearance overestimates GFR due to tubular secretion of creatinine. This secretion is present even in patients with significantly reduced glomerular filtration rates. As a consequence, the lower the GFR the higher the overestimation will be. 3. A good correlation was obtained between the Cr-51-EDTA and inulin clearance: y(EDTA) = 4.21 + 0.88 x (inulin), r = 0.98. The procedure is simple to perform, and the radiotracer utilized is significantly less expensive than iothalamate.