Renal Function Assessment in the Elderly Using Plasma Creatinine Assay and Lean Body Mass Measurement

Renal Function Assessment in the Elderly Using Plasma Creatinine Assay and Lean Body Mass Measurement

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.

Muscular mass is closely linked to lean body mass (LBM), which can be properly assessed by whole-body dual X-ray absorptiometry (DXA). Alternatively, Bioelectric Impedance Spectroscopy (BIS) can also be used.

Investigators postulate that it is possible to estimate GFR in the elderly from both SCr and LBM estimation from DXA. Proof of concept has already been made by others but until now, no specific formula for the elderly has been devised and properly validated.

Investigators'aim is thus to propose a new formula to predict GFR from both SCr and LBM (estimated from DXA) in the elderly. This formula will be elaborated from a first series of 100 patients and validated on a second series of 100 other patients.

Inclusion criteria :

• age of 75 years of more
• origin from Western Europe or North Africa
• covered by social health insurance
• general health condition allowing transportation and ambulatory procedures during one day

Exclusion criteria :

• ascitis, oedema or third compartment

• fast change in body weight (more than 5% in less than one week)

• eGFR < 30 mL/min/1.73 m² (using MDRD formula)

• legal concerns: prisoners, guardianship, lack of health insurance, failure to consent

• intake of drugs that interfere with creatinine tubular secretion

  • cimetidine
  • trimethoprim

• intake of drugs that interfere with creatinine assay

  • calcium dobesilate
  • hydroxocobalamin
  • N-ethylglycine
  • phenindione
  • lidocaine

• inability to lie during 10 minutes without moving

• patients who are bedridden, hemiplegic or highly dependent on others

• any health condition that, in the investigator's opinion, could rapidly (< 1 week) vary the extracellular volume or GFR (these is voluntarily left open to the investigator because it is hardly possible to make an exhaustive list here)