QJM Advance Access originally published online on May 15, 2007
QJM 2007 100(6):390-391; doi:10.1093/qjmed/hcm038
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Estimated glomerular filtration rates (eGFR): predicting progression is dependent on accuracy
Sir,In a recent paper, Hemmelgarn et al. introduced a potentially important clinical risk score for the prediction of progression amongst patients with chronic kidney disease (CKD).1 The use of readily available clinical data to allow risk stratification of patients would represent a significant advance in the practical management of CKD. However, the study has a number of potentially problematic methodological issues. The authors chose to limit their study population to those with an eGFR <90 ml/min/1.73 m2, because of concerns regarding the validity of the MDRD eGFR estimate above that level of function.2 These validity concerns continue to be a problem when using the MDRD estimation equation between 60 and 90 ml/min/1.73 m2, and this concern has become so prominent within the nephrology community that the equation's creators have recommended reporting eGFR estimates as simply >60 ml/min/1.73 m2, rather than giving specific estimates above that level.3
Recent advances have improved the accuracy of the MDRD equation (traceable by isotope dilution mass spectrometry IDMS),4 but (as recently discussed in QJM) these corrections are dependent on central laboratory validation and provision of correction factors.5 Regardless of the methodology, there remains significant concern over the clinical relevance of an estimated GFR between 60 and 90 ml/min/1.73 m2, particularly in the elderly female population. Including these patients in the analysis increases the likelihood of misclassifying anomalies in creatinine measurement and eGFR estimation as progression. Previous studies have indicated the potential variance of eGFR estimation in the same person over time within the same laboratory, and more recently we have come to realize the impact of simple daily activities, such as a cooked meal,6 on eGFR estimations.
In epidemiological studies assessing CKD progression, it is crucial to limit methodological errors in creatinine measurement and eGFR estimation, if we are to gain a reliable understanding of the natural history of CKD.7,8 Cystatin C may represent the most exciting potential solution to estimating renal function accurately in early CKD, but its expense and lack of availability currently limit its use; until this changes, we must be aware of the limitations of our currently used estimates.
The Queen's University
Belfast
email: mquinn05{at}qub.ac.uk
References
1. Hemmelgarn BR, Culleton BF, Ghali WA. Derivation and validation of a clinical index for prediction of rapid progression of kidney dysfunction. Q J Med (2007) 100:87–92.[Web of Science]
2. Stevens LA, Coresh J, Greene T, Levey AS. Assessing kidney function—measured and estimated glomerular filtration rate. N Engl J Med (2006) 354:2473–83.
3. Levey AS, Coresh J, Greene T, Marsh J, Stevens L, Kusek J, et al. Expressing the MDRD Study Equation for Estimating GFR with IDMS Traceable (Gold Standard) Serum Creatinine Values. J Am Soc Nephrol (2005) 16:69A.[CrossRef]
4. Levey AS, Coresh J, Van Lente F. Letters, Estimated Glomerular Filtration Rate, In Response. Ann Int Med (2007) 146:74–5.
5. Miller G, Myers GL, Eckfeldt JH, Greenberg N. Calculating eGFR using the MDRD equation. Q J Med (2007) 100:142–3.[Web of Science]
6. Preiss DJ, Godber IM, Lamb EJ, Dalton RN, Gunn IR. The influence of a cooked-meat meal on estimated glomerular filtration rate. Ann Clin Biochem (2007) 44:35–42.[CrossRef][Web of Science][Medline]
7. McKillop DJ, Cairns B, Duly E, Van Drimmelen M, Ryan M. The effect of serum creatinine method choice on estimated glomerular filtration rate determined by the abbreviated MDRD formula. Ann Clin Biochem (2006) 43:220–2.[CrossRef][Web of Science][Medline]
8. Wang X, Lewis J, Appel L, et al. Validation of creatinine-based estimates of GFR when evaluating risk factors in longitudinal studies of kidney disease. J Am Soc Nephrol (2006) 17:2900–9.
CiteULike 
Connotea 
Del.icio.us What's this?
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||