Reassessment of a classical single injection 51Cr-EDTA clearance method for determination of renal function in children and adults. Part II: Empirically determined relationships between total and one-pool clearance.

Background . The one-pool or slope-intercept technique is widely used when determining total 51Cr-EDTA plasma clearance (Cl). The one-pool clearance (Cl 1), which always exceeds Cl, has mostly been corrected to Cl by multiplication by a constant factor = 0.80, suggested by Chantler (CH0.80), or by using a second-order polynomial originally proposed by Brøchner-Mortensen (BM) and later recommended by the British Nuclear Medicine Society (BMBNMS). Theoretical considerations indicate that the CH correction gives a systematic overestimate of Cl, whereas the BM correction may underestimate Cl at high values. Objective . To assess the accuracy of Cl as estimated from Cl 1 corrected either by CH0.80 or by second-order polynomials. Material and methods . Clref was determined in 149 subjects (M/F/children: 71/46/32) from a complete plasma curve followed for 4-5 h after injection of 51Cr-EDTA (range of Clref : 8-183 mL/min/1.73 m2). Clest was determined from Cl 1 subsequently corrected by CH0.80 and four second-order polynomials. Results . Using CH0.80 correction, Clest underestimated Clref (by a maximum of 20 %) at Clref values less than about 100 mL/min/1.73 m2 in children and 130 mL/min/1.73 m2 in adults. At higher clearance levels, Clref was increasingly overestimated. Taking the BMBNMS correction as representative of second-order polynomials, Clest increasingly underestimated Clref at high levels, the error being 10 % at a Clref value of about 175 mL/min/1.73 m2. Conclusions. We suggest that the tested correction equations are replaced by the given common correction equation based on the “true” relationship between Cl 1 and Cl thoroughly described in part I of this study. [ABSTRACT FROM AUTHOR]