Assessment of renal function in elderly after eighty years: Cockroft and Gault or Modification of diet in renal disease equation?

Assessment of renal function is essential in the management of hospitalised patients, particularly in geriatric practice. Impairment of renal function is common in the elderly, aged of 80 years and over, and should be taken into account before prescribing drugs eliminated through the kidneys or performing investigations requiring iodine injection. Renal failure is also a predictor of mortality. In clinical practice, creatinine-based equations are recommended to assess kidney function. The most widely used equations are the Cockroft and Gault (CG) and the simplified Modification of diet in renal disease (MDRD) formulas. The former estimates the clearance of creatinine in millilitres per minute, the latter estimates the glomerular filtration rate in millilitres per minute per 1.73 m(2). In 2002, the French high authority for health recommended the use of the CG formula, but no recommendation was given for the elderly. In the literature, no study has compared CG and MDRD formulas with a reference method in this very old population. In the octogenarians, two studies have compared these formulas with the creatinine clearance calculated on the basis of a 24-hour urine collection and four studies have compared the formulas head to head. All these studies showed that the results obtained with the MDRD formula are higher from 10 to 30 mL/min/1.73 m(2) than the results obtained with the CG formula. Studies simulating drug prescription showed that: the use of the MDRD formula would lead to a risk of drug over dosage in 20 to 36% of the elderly. Also, two studies have suggested that only creatinine clearance measured by the CG formula is a predictor of mortality in the very old population. In conclusion, in the octogenarian, none of these two formulas is ideal. However, based on the results of studies targeted to this elderly population, the best solution seems to be the use of the CG formula expecting new methods of evaluation of renal function. (C) 2011 Published by Elsevier Masson SAS on behalf of the Societe nationale francaise de medecine interne (SNFMI).