Volume 188 - Issue 7
Chronic kidney disease and automatic reporting of estimated glomerular filtration rate: revised recommendations
Author: William R Adam
Med J Aust 2008; 188 (7): 427-430. || doi: 10.5694/j.1326-5377.2008.tb01698.x
Published online: 7 April 2008
Published online: 7 April 2008
To the Editor: The revised recommendations of the Australasian Creatinine Consensus Working Group1 are improved with the recognition of an age-related reduction in glomerular filtration rate (GFR), but don’t deal with a number of other significant problems associated with an estimated GFR (eGFR).
When a plasma creatinine measurement is requested, an eGFR is commonly provided, increasing the sensitivity but reducing the specificity of diagnosis of kidney disease. The eGFR remains a substantially flawed estimate of GFR. It is associated with significant predictive error (up to 30% of individual eGFRs differ by more than 30% from the measured GFR at 60–90 mL/min)2 and with substantial false positive and false negative outcomes.
The flaws in the eGFR are, firstly, the limitations of creatinine clearance rate as a measure of GFR, and secondly (and more importantly), the use of age, sex and race as surrogates for muscle mass (the determining factor in creatinine production and, together with creatinine clearance, plasma creatinine level).
Age, sex and race are imperfect predictors of muscle mass, and this leads to underestimation of GFR in people who are fit and well muscled and overestimation in those who are wasted and disabled. While reporting eGFR values represents a worthwhile advance on using plasma creatinine levels to detect kidney disease, it could be considered, at best, the “least bad” readily available measure of GFR.
When no better test is readily available, how should we handle a suboptimal measure of GFR? Educating the medical profession about the limitations of eGFR is important, but, based on personal experience and anecdotal evidence, I believe that using conventional methods of informing doctors has not been uniformly effective. Providing “just in time” information support is likely to assist this process.
Thus, I support the recommendation that laboratories routinely report eGFRs, but suggest that, when they do so, they add a product warning along the following lines:
The eGFR is calculated assuming a normal muscle mass for age, sex and race. It will underestimate GFR in well muscled individuals and overestimate GFR in patients with muscle wasting. A creatinine clearance test or formal GFR measurement may be helpful in patients whose muscle mass differs from the average for their age and sex. Proteinuria and haematuria are other useful indicators of kidney disease.
In patients over 70 years of age, an additional product warning, consistent with the Australasian Creatinine Consensus Working Group’s revised recommendations,1 could be as follows:
References
- Mathew TH, Johnson DW, Jones GRD, on behalf of the Australasian Creatinine Consensus Working Group. Chronic kidney disease and automatic reporting of estimated glomerular filtration rate: revised recommendations. Med J Aust 2007; 187: 459-463. 0_CBBHGHAB
- Poggio ED, Wang X, Greene T, et al. Performance of the Modification of Diet in Renal Disease and Cockcroft–Gault equations in the estimation of GFR in health and in chronic kidney disease. J Am Soc Nephrol 2005; 16: 459-466. 0_i1091827