Estimating renal function in older people: a comparison of three formulas
1 Cattedra di Geriatria, Università Campus Biomedico, Roma, Italy
2 Dipartimento di Medicina Geriatrica, Istituto Nazionale di Ricovero e Cura per Anziani (INRCA), I-87100 Cosenza, Italy
Address correspondence to: A. Corsonello, Via d. Frugiuele 39, I-87100 Cosenza, Italy. Tel: (+39) 984 68 21 11. Fax: (+39) 984 46 18 72. Email: andrea_corsonello{at}tin.it
Background: estimation of the glomerular filtration rate (GFR) at the bedside is important because renal insufficiency is related to increased mortality and morbidity. A discrepancy between the Cockroft–Gault (CG) and the Modification of Diet in Renal Disease (MDRD) formulas has been observed in older people.
Objective: to compare the GFR of inpatients aged 65 or older estimated using the CG and two of the MDRD formulas.
Setting: acute care geriatrics and internal medicine wards.
Subjects and methods: data come from the Gruppo Italiano di Farmacovigilanza nell’Anziano (GIFA). To quantify the agreement between the formulas, we used the 95% limits of agreement, the 
statistic and a graphic approach to evaluate the influence of potential confounders on the magnitude of the difference in the GFR estimates.
Results: we studied 7,747 persons [51.1% women, mean age 77.8 (SD 7.2)]. The mean GFR estimated using the CG, MDRD1 and MDRD2 formulas was 51.2 ml/min (21.3), 54.9 ml/min (19.8) and 64.7 ml/min (24.2), respectively. At the individual level, the MDRD formulas can yield estimates that differ by more than 50% compared with the CG formula. The formulas showed a moderate agreement in diagnosing moderate renal insufficiency and a fair agreement in diagnosing severe renal insufficiency. The magnitude of the difference in GFR estimates was influenced by age and weight.
Conclusions: the CG and MDRD formulas have a good average agreement, but at the individual level, they can give estimates that differ substantially, and cannot be used interchangeably to measure renal function in elderly people.
Keywords: aged, aged 65 and over, renal failure, estimating formulas, elderly
Received August 1, 2005; accepted in revised form December 6, 2005.
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