Renal function equations before and after living kidney donation: a within-individual comparison of performance at different levels of renal function.
OBJECTIVE
The Modification of Diet in Renal Disease (MDRD) study equation and the Cockcroft-Gault (CG) equation perform poorly in the (near-) normal range of GFR. Whether this is due to the level of GFR as such or to differences in individual characteristics between healthy individuals and patient with chronic kidney disease (CKD) is unknown.


METHODS
We evaluated the performance of MDRD, CG per BSA (CG/(BSA)) and Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equations compared with measured GFR (mGFR; I-iothalamate) at 4 months before and 2 months after donation in 253 consecutive living kidney donors.


RESULTS
mGFR declined from 103 ± 15 to 66 ± 11 ml/min per 1.73 m(2) after donation. All equations underestimated mGFR at both time points. Arithmetic performance analysis showed improved performance after donation of all equations, with significant reduction of bias after donation. Expressed as percentage difference, mGFR-estimated GFR (eGFR) bias was reduced after donation only for CG/(BSA). Finally, in 295 unselected individuals who were screened for donation, mGFR was below the cutoff for donation of 80 ml/min per 1.73 m(2) in 19 individual but in 166, 98, and 74 for MDRD, CDK-EPI, and CG/(BSA), respectively.


CONCLUSIONS
A higher level of GFR as such is associated with larger absolute underestimation of true GFR by eGFR. For donor screening purposes, eGFR should be interpreted with great caution; when in doubt, true GFR should be performed to prevent unjustified decline of prospective kidney donors.
Tent
Hilde
H
Department of Internal Medicine, Division of Nephrology, University Medical Center Groningen, Groningen, Netherlands. h.tent@int.umcg.nl
Rook
Mieneke
M
Stevens
Lesley A
LA
van Son
Willem J
WJ
van Pelt
L Joost
LJ
Hofker
H Sijbrand
HS
Ploeg
Rutger J
RJ
van der Heide
Jaap J Homan
JJ
Navis
Gerjan
G
D000328:Adult; D015415:Biomarkers / Q000097:blood; D001794:Blood Pressure; D001830:Body Surface Area; D001835:Body Weight; D002908:Chronic Disease; D003404:Creatinine / Q000097:blood; D046148:Donor Selection; D005260:Female; D005919:Glomerular Filtration Rate; D006305:Health Status Indicators; D006801:Humans; D007483:Iothalamic Acid; D007668:Kidney / Q000503:physiopathology / Q000601:surgery*; D007674:Kidney Diseases / Q000503:physiopathology / Q000601:surgery*; D016030:Kidney Transplantation; D019520:Living Donors; D008297:Male; D008875:Middle Aged; D008954:Models, Biological; D009426:Netherlands; D011237:Predictive Value of Tests; D012044:Regression Analysis; D012737:Sex Factors; D013997:Time Factors; D016896:Treatment Outcome
D015415:Biomarkers; D007483:Iothalamic Acid; D003404:Creatinine