Relationship of creatinine clearance to orthoiodohippurate measured effective renal plasma flow

Effective renal plasma flow (ERPF) was measured utilizing 1-131 orthoiodohippurate (OIH). The OIH ERPF was correlated in 50 patients with routine 24-hour urine creatinine clearance measurements and with a formula predicting creatinine clearance based on age, weight, and serum creatinine (formula creatinine clearance). The filtration fraction (routine creatinine clearance/OIH ERPF) in 38 patients with hypertensive nephrosclerosis, tubulointerstitial renal disease, or normal renal function were compared. Filtration fractions in the three groups tested were not statistically different. ERPF had a correlation coefficient of 0.62 with routine creatinine clearance and 0.72 with formula creatinine clearance. Thus, OIH ERPF correlates with creatinine clearance measurements but cannot be used to replace creatinine clearance as a method of evaluating renal function. The reasons for the lack of a stronger positive correlation between ERPF and glomerular filtration rate (GFR) remain to be elucidated.