Journal Information
Vol. 28. Issue. 2.April 2008
Pages 123-238
Vol. 28. Issue. 2.April 2008
Pages 123-238
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Serum creatinine is a more useful tool for the evaluation of renal function in the ederly as than calculating the glomerular filtratio rate
La creatinina plasmática una herramienta más útil que los cálculos de filtrado glomerular para la evaluación de la función renal en ancianos
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Manuel Heras Benitoa, M. J.. Fernández- Reyesa, R.. Sánchez Hernándeza, M. T.. Guerrero Díazb
a Servicio de Nefrología, Hospital General de Segovia, Segovia, España,
b Servicio de Geriatría, Hospital General de Segovia, Segovia, España,
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To the editor:

The simple calculation of the glomerular filtration rate (GFR) from mathematical formulations using the serum creatinine value (sCr), sometimes even being directly provided by the Laboratory, and the convenience of not having to collect 24-hour urine, has allowed health professionals to classify chronic renal disease (CRD) in several stages.1-2.

Standardized determination of GFR by means of mathematical formulations in the whole population may yield low GFR values with unclear usefulnees in clinical practice.

An example of the low reliability of these mathematical formulations is their indiscriminate use in the elderly. We have performed a cross-sectional study on 80 elderly people (mean age 82.4 ± 6 years; 31% males; 81% high blood pressure; 37.3% diabetes mellitus), who were stable with different sCr values (range 0.7-3 mg/dL). The aim was to assess the GFR in this population and determine whether the decrease in GFR < 60 mL/min (stages III-IV) is related to the analytical alterations associated to CRD. We measured the following blood values: acid-base balance, calcium, phosphorus, ions, urea, and blood cell count. A urinalysis was also performed. The GFR was calculated by means of the Cockcroft-Gault3 and MDRD4 equations.

Mean GFR calculated by Cockcroft¿ s equation was 39 ± 14 mL/min and by MDRD was 51 ± 16 mL/min. According to the K-DOQI classification, a GFR < 60 is categorized as stage 3 chronic renal disease. Since all the patients in our study had global mean GFR < 60 mL/min (with both formulations), they ought to be classified at least as stage 3 CRD.

The sCr values correlate with urea (r: 0.73, p < 0.001), uric acid (r: 0.46, p < 0.001), calcium (r: -0.24, p = 0.032) and potassium (r: 0.26, p = 0.021).

Cockroft formulation correlates with sCr values (r: -0.67, p < 0.001), urea (r: -0.61, p < 0.001) and MDRD correlates with sCr values (r: -0.84, p < 0.001), urea (r: -0.68, p < 0.001), uric acid (r: -0.48, p < 0.001) but none of them correlates with other typical alterations of CRD.

In summary, the elderly have a diminished GFR inherent to the aging process, and the GFR determination with the formulations do not seem to offer any advantage from simple sCr determination. We absolutely agree with the sceptic vision of Dr. Robles about the GFR calculation, presented in an article published in your journal.5

Bibliography
[1]
De Jong PE, Halbesma N, Gansevoort RT. Screening for early chronic kidney diseasewhat method fits best? Nephrol Dial Transplant 2006; 21: 2358-2361.
[2]
Levey AS, Coresh J, Balk E y cols. National Kidney Foundation Practice Guidelines for Chronic Kidney Disease: evaluation, classification and stratification. Ann Intern Med 2003; 139: 137-147. [Pubmed]
[3]
Cockroft DW, Gault MH. Prediction of creatinine clearance from serum creatinine. Nephron 1976; 16: 31-41. [Pubmed]
[4]
Levey AS, Greene T, Kusek JW, Beck GJ. Simplified equation to predict glomerular filtration rate from serum creatinine. J Am Soc Nephrol 2000; 11: 828 (A).
[5]
Robles NR. Cálculo de filtrado glomerular: una visión escéptica. Nefrología 2007; 27(4): 405-407. [Pubmed]
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