In their paper, Marx et al. comment that our group have also shown the Wright formula to be superior over the CockroftGault and Jelliffe formulae [3]. In our study this was correct when comparing the various formulae over all ranges of GFR; however, we actually showed that the Wright formula did have a significant positive bias for low GFR (i.e. overestimates) and a significant negative bias for high GFR (i.e. underestimates). This led us to conclude in our paper that the Wright formula provides a biased and imprecise estimate of GFR. This interpretation is further supported in that we have recently analysed data on 525 patients (as yet unpublished) who have had GFR determined by Tc99m DTPA clearance at our centre. In this group there were 41 patients >70 years of age with a GFR <50 ml/min. The mean percentage error of the Wright formula was 26.5% (95% confidence interval 13.1% to 39.8%). Consequently, we cannot recommend the use of the Wright formula. From a clinical perspective, a tool is needed that provides a reliable estimate across the full range of renal function. Our data, and possibly that of Marx et al. [1
], indicate that the Wright formula has substantially limited applicability.
Further research is required to develop reliable methods of bedside estimates of GFR, as there is no precise formula available. Recently, the Modification of Diet in Renal Disease formula has been advocated, but this too requires validation in cancer patients with poor renal function [4, 5
].
1 Peter MacCallum Cancer Centre, St Andrews Place, East Melbourne, 8006 Melbourne; 2 Department of Pharmacy Practice, Monash University, Victoria, Australia
Email: m.dooley{at}alfred.org.au)
References
1. Marx GM, Blake GM, Steer CB et al. Evaluation of the Cockcroft-Gault, Jelliffe and Wright formulae in estimating renal function in elderly cancer patients. Ann Oncol 2004; 15: 291295.
2. Wright JG, Boddy AV, Highley M et al. Estimation of glomerular filtration rate in cancer patients. Br J Cancer 2001; 84: 452459.[CrossRef][ISI][Medline]
3. Poole SG, Dooley MJ, Rischin D. A comparison of beside renal function estimates and measured glomerular filtration rate (Tc99m DTPA clearance) in cancer patients. Ann Oncol 2002; 13: 949955.
4. Levey AS, Bosch JP, Breyer LJ et al. A more accurate method to estimate glomerular filtration rate from serum creatinine: A new prediction equation. Ann Intern Med 1999; 130: 461470.
5. Murray PT, Ratian MJ. Estimation of the glomerular filtration rate in cancer patients: a new formula for new drugs. J Clin Oncol 2003; 21: 26332635.
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