NDT Advance Access originally published online on August 28, 2008
Nephrology Dialysis Transplantation 2009 24(1):109-116; doi:10.1093/ndt/gfn477
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Longitudinal analysis of performance of estimated glomerular filtration rate as renal function declines in chronic kidney disease
1 Department of Nephrology, Western Hospital, Melbourne, Victoria, Australia 2 Department of Nephrology, St Paul's Hospital, Vancouver, BC, Canada 3 Department of Renal Medicine, Gosford Hospital, Gosford, New South Wales, Australia
Darren Lee, Department of Nephrology, Austin Health, Studley Road, Heidelberg, VIC 3084, Australia. Tel: +61-3-9496-5000; Fax: +61-3-9496-5123; E-mail: vrsadhkl{at}hotmail.com
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Abstract |
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Background. Numerous studies have assessed the accuracy of equations estimating glomerular filtration rate (eGFR) from serum creatinine in individuals with chronic kidney disease (CKD) in cross-sectional studies. Limited literature exists, however, on the consistency of performance of these equations in longitudinal studies as renal function declines.
Methods. Radionucleotide-measured GFR from 155 predialysis patients with stage 3–5 CKD was compared with eGFR derived from four equations [6-variable Modification of Diet in Renal Disease (6-MDRD), 4-variable MDRD (4-MDRD), Cockcroft–Gault (CG) and Cockcroft–Gault equations corrected for body surface area (CGC)] at baseline, 12 and 24 months. Bias (difference between eGFR and measured GFR) was used as a measure of performance. Restricted Maximum Likelihood (REML) models were used to identify variables potentially affecting the performance of estimating equations across time.
Results. Mean measured GFR (±SD) at baseline, 12 and 24 months was 25.9 ± 10.7, 23.1 ± 10.6 and 20.3 ± 10.1 mL/min/1.73 m2, respectively. There was a statistically significant negative association between bias and GFR for all four estimates (range: –0.76 to –0.71, P < 0.001 for all), indicating worsening underestimation and overestimation at higher and lower GFR, respectively. This negative association significantly reduced over the 24 months (P < 0.001); however, this was largely due to persistent underestimation of eGFR from individuals with GFR >50 mL/min/1.73 m2. For those with a baseline GFR <50 mL/min/1.73 m2, the change in bias for any of the four equations over 24 months was 
1.1 mL/min/1.73 m2, suggesting relatively preserved performance with time. The MDRD equations showed a sustained advantage in estimating renal function that was more evident as GFR declined.
Conclusion. GFR estimates are inexpensive and show an acceptable longitudinal performance for monitoring CKD patients with GFR <50 mL/min/1.73 m2. Inaccuracies appear more substantial above this level of GFR, and care with interpretation is required.
Keywords: Cockcroft–Gault; eGFR; longitudinal; MDRD
Received for publication: 20. 4.08
Accepted in revised form: 31. 7.08