IN CLINICAL investigations requiring estimation of glomerular filtration rate (GFR), it is desirable that the technique employed be both reliable and convenient. The clearance of inulin is generally accepted as the most accurate method for measuring rate of glomerular filtration. In prolonged studies, however, the frequent or serial determination of inulin clearance presents certain problems of convenience to both investigator and patient and it would be highly advantageous if some simple but equally reliable method was available.
The search for a convenient clinical method has centered principally upon the clearance of urea and creatinine. Urea was discarded when its rate of clearance was shown to be less than inulin and dependent upon rate of urine flow.1 Endogenous creatinine is a normal end-product of creatine metabolism.2 Its daily production and urinary excretion in normal subjects is relatively proportional to lean body mass.2-4 Our findings are consistent with the