A comparison of the plasma disappearance of iohexol and 99mTc-DTPA for the measurement of glomerular filtration rate (GFR) in diabetes.
BACKGROUND
Changes in glomerular filtration rate (GFR) provide a valuable indicator of the progression of diabetic nephropathy. GFR is most commonly measured by the plasma clearance of radioisotopes, however, use of iohexol, a non-ionic radiocontrast medium, is a recently described alternative and has shown good agreement with inulin clearance. A one-compartment model is used for calculating GFR in most Australian centres but a two-compartment model is more accurate.


OBJECTIVE
To set up a non-radioisotopic method for assessment of GFR using iohexol, and to compare this with the currently used 99mTc-diethylene-triamine-penta-acetic acid (DTPA) method. Secondly, to compare GFR results using an unmodified one-compartment model with a one-compartment model subjected to the Brochner-Mortensen modification.


METHODS
Twenty-one patients with diabetes had assessment of GFR with simultaneous measurements of 99mTc-DTPA and iohexol plasma clearance. Plasma clearance was determined by the slope intercept method and then modified according to the Brochner-Mortensen equation. Plasma iohexol concentrations were determined by capillary electrophoresis.


RESULTS
There was no significant difference between iohexol and 99mTc-DTPA derived GFR values, difference 4.3+/-7.7 mL/minute (mean+/-SD). This was despite 99mTc-DTPA protein binding demonstrated in the range of 5-10%. Comparison of GFR results using an unmodified one-compartment model with a Brochner-Mortensen corrected one-compartment model showed higher GFR values with the former, in the range of 20-30% for GFR values > 100 mL/minute.


CONCLUSIONS
Iohexol provides an efficient alternative to radioisotopic methods for serial measurement of GFR in diabetic patients with hyperfiltration, incipient and overt nephropathy. A one-compartment model with its inherent overestimation of GFR should be replaced by the Brochner-Mortensen modified one-compartment model.
Houlihan
C
C
Department of Medicine, University of Melbourne, Austin and Repatriation Medical Centre, Vic.
Jenkins
M
M
Osicka
T
T
Scott
A
A
Parkin
D
D
Jerums
G
G
D000328:Adult; D000368:Aged; D003287:Contrast Media; D003920:Diabetes Mellitus / Q000097:blood / Q000503:physiopathology*; D019075:Electrophoresis, Capillary; D005260:Female; D005919:Glomerular Filtration Rate; D006801:Humans; D007472:Iohexol; D008297:Male; D008657:Metabolic Clearance Rate; D008875:Middle Aged; D016284:Technetium Tc 99m Pentetate / Q000097:blood
D003287:Contrast Media; D007472:Iohexol; D016284:Technetium Tc 99m Pentetate