 Glomerular filtration rate GFR is the recommended parameter to assess renal function. The reference technique to measure GFR clearance of a glomerular agent is not commonly used. Instead, estimations eGFR are routinely taken from serum creatinine SCr with several published formulae: Cockcroft and Gault, MDRD, CKD-EPI. Basically, all these formulae aim at predicting the endogenous creatinine production by morphological parameters age, body weight... However, in the elderly, muscular mass is extremely variable and sarcopenia is quite commonly encountered frequently linked to Alzheimer disease. This is probably the main reason why the aforementioned formulae are not valid in this population: for a given renal function, a lower muscular mass induces a lower creatinine production and, henceforth, a lower SCr value, which gives an overestimation of eGFR. 