Extrarenal plasma clearance of iohexol, chromium-51-ethylenediaminetetraacetic acid, and inulin in anephric pigs.
OBJECTIVE
To improve the measurement of the glomerular filtration rate (GFR), we determined the extrarenal plasma clearance of the GFR markers iohexol, chromium-51-ethylenediaminetetraacetic acid (51Cr-EDTA), and inulin using 11 anephric pigs.


METHODS
After an intravenous (i.v.) bolus injection of the markers, the decay curves of their plasma concentrations were monitored for 29 hr by 16 plasma samples. The area under the curve (AUC; concentration of marker versus time) was calculated according to one- and three-compartment kinetics. The extrarenal clearance was calculated by dividing the dose of marker by the AUC.


RESULTS
In the three-compartment model, the median of the extrarenal clearances of iohexol, 51Cr-EDTA, and inulin were 0.87 ml.min-1.10 kg-1 (range = 0.62-1.26 ml.min-1.10 kg-1), 0.79 ml.min-1.10 kg-1 (range = 0.61-1.04 ml.min-1.10 kg-1), and 0.83 ml.min-1.10 kg-1 (range = 0.65-1.17 ml.min-1.10 kg-1). The extrarenal clearance of 51Cr-EDTA was slightly lower than that of iohexol and inulin when measured with the three-compartment model (p = .015). There was no statistically significant difference between the two models of kinetics in calculating clearance of the same marker.


CONCLUSIONS
Our results indicate that subtracting the median values of the extrarenal clearance of the markers from the total plasma clearance will provide GFR values closer to the "true" GFR. This technique might prove useful in GFR calculations in patients with a very low GFR (e.g., residual GFR in patients on dialysis).
Frennby
B
B
Department of Diagnostic Radiology, University of Lund, Malmö University Hospital, Sweden.
Sterner
G
G
Almén
T
T
Chai
C M
CM
Jönsson
B A
BA
Månsson
S
S
D000818:Animals; D002860:Chromium Radioisotopes / Q000493:pharmacokinetics; D003287:Contrast Media / Q000493:pharmacokinetics; D004492:Edetic Acid / Q000493:pharmacokinetics*; D005919:Glomerular Filtration Rate; D007444:Inulin / Q000493:pharmacokinetics*; D007472:Iohexol / Q000493:pharmacokinetics*; D008657:Metabolic Clearance Rate; D009392:Nephrectomy; D013552:Swine
D002860:Chromium Radioisotopes; D003287:Contrast Media; D007472:Iohexol; D007444:Inulin; D004492:Edetic Acid