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

Abstract

Background. The one‐pool or slope‐intercept technique is widely used when determining total ⁵¹Cr‐EDTA plasma clearance (Cl). The one‐pool clearance (Cl₁), 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 Cl₁ 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 ⁵¹Cr‐EDTA (range of Cl_ref: 8–183 mL/min/1.73 m²). Cl_est was determined from Cl₁ 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 m² in children and 130 mL/min/1.73 m² 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 m². Conclusions. We suggest that the tested correction equations are replaced by the given common correction equation based on the “true” relationship between Cl₁ and Cl thoroughly described in part I of this study.

• ⁵¹Cr‐EDTA
• glomerular filtration rate
• plasma clearance
• renal function
• slope‐intercept technique