Background: The one-pool or slope-intercept technique is widely used when determining total (51)Cr-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 (CH(0.80)), or by using a second-order polynomial originally proposed by Brøchner-Mortensen (BM) and later recommended by the British Nuclear Medicine Society (BM(BNMS)). 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 CH(0.80) or by second-order polynomials.
Material and methods: Cl(ref) was determined in 149 subjects (M/F/children: 71/46/32) from a complete plasma curve followed for 4-5 h after injection of (51)Cr-EDTA (range of Cl(ref) : 8-183 mL/min/1.73 m(2)). Cl(est) was determined from Cl(1) subsequently corrected by CH(0.80) and four second-order polynomials.
Results: Using CH(0.80) correction, Cl(est) underestimated Cl(ref) (by a maximum of 20%) at Cl(ref) values less than about 100 mL/min/1.73 m(2) in children and 130 mL/min/1.73 m(2) in adults. At higher clearance levels, Cl(ref) was increasingly overestimated. Taking the BM(BNMS) correction as representative of second-order polynomials, Cl(est) increasingly underestimated Cl(ref) at high levels, the error being 10% at a Cl(ref) value of about 175 mL/min/1.73 m(2).
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.