Reassessment of a classical single injection 51Cr-EDTA clearance method for determination of renal function in children and adults. Part I: Analytically correct relationship between total and one-pool clearance.
BACKGROUND
Total plasma clearance of (51)Cr-EDTA, Cl, is widely used as a measure of GFR. Commonly, only the final part of the plasma concentration curve is measured, and a one-pool clearance (slope-intercept clearance), Cl(1), is computed. Empirically determined second-order polynomials of the general form Cl = b x Cl(1) + c x Cl(1)(2) are usually used to estimate Cl from a measured Cl(1). However, theoretical considerations indicate that such corrections underestimate Cl at high values.


OBJECTIVE
To derive an analytically correct relationship between Cl and Cl(1) and determine the parameters involved for children and adults.


METHODS
Cl was determined in 149 subjects (M/F/children: 71/46/32) from a complete plasma concentration curve followed for 4-5 h after injection of (51)Cr-EDTA (range of clearance: 8-183 mL/min/1.73 m(2)). Plasma volume, PV and the "missing" area under the plasma fraction curve, a (minutes), not used for determination of Cl(1), were measured.


RESULTS
The true relationship between Cl and Cl(1) is given by Cl = Cl(1)/(1 + f x Cl(1)), where f = a/PV. For men, women and children alike, the equation f = 0.0032 x BSA(-1.3) was applicable (BSA = body surface area in m(2)). Estimation errors on clearance were within +/-8% for adults and +/-13% for children (95% limits of agreement).


CONCLUSIONS
The true relationship between Cl and Cl(1) of (51)Cr-EDTA is given, resulting in a common correction equation applicable for children and adults. The new equation has better mathematical behaviour than quadratic equations on very high values of clearance and takes into account dependence on body size.
Jødal
Lars
L
Department of Nuclear Medicine and Center for Cardiovascular Research, Aalborg Hospital, Aarhus University Hospital, Aalborg, Denmark. lajo@rn.dk
Brøchner-Mortensen
Jens
J
D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001830:Body Surface Area; D002648:Child; D002675:Child, Preschool; D004492:Edetic Acid / Q000008:administration & dosage / Q000493:pharmacokinetics*; D005260:Female; D006801:Humans; D007223:Infant; D007267:Injections; D007677:Kidney Function Tests / Q000379:methods*; D008297:Male; D008657:Metabolic Clearance Rate; D008875:Middle Aged; D008954:Models, Biological; D010953:Plasma Volume; D055815:Young Adult
D004492:Edetic Acid