The measurement of GFR is not feasible to clinical practice. Serum creatinine (SCr) is a simple marker of GFR impairment, unfortunately it lacks sensitivity, particularly in aged patients. Different formulas have been proposed to predict GFR from SCr, avoiding 24-hour urinary collection which is a major problem in aged patients.
The aim of this study was to evaluate a new method to predict GFR in aged patients from the body cell mass (BCM) and SCr, avoiding urine collection.
Patients and Methods
Eighty adult chronic kidney disease (CKD) patients (43 males), aged 65-81 years, mean 71, with different renal function (SCr 0.7-8.8mg/dL) participated in this study. GFR was measured as the renal clearance of 99mTc-DTPA. SCr was determined with a standard laboratory method. The values of BCM were obtained by means of body impedance analysis, with a single frequency impedance analyzer.
The relationship of GFR with Scr and BCM demonstrated a very high correlation between GFR and the ratio BCM/SCr. Form this relationship we derived a formula to predict GFR from the values of SCr and BCM:
BCMGFR(mL/min) = Patient’s BCM (kg) x 2.69 / SCr (mg/dL).
For comparison, GFR was predicted also according to Cockcroft and Gault formula (CGGFR), and to the simplified MDRD formula (MDRDGFR).
BCMGFR gave the most precise estimate of GFR [figure1]. In fact, BCMGFR had the best agreement with true GFR (99mTc-DTPA), while CGGFR and MDRDGFR significantly overestimated true GFR. The coefficients of variation of all prediction formulas were markedly lower than that of 24h CCr (22.4%). Finally, the error of prediction of BCMGFR was definitely lower than that of CGGFR and MDRDGFR.
In aged patients, GFR can be predicted from the values of BCM and serum creatinine. In the mean time, the impedance analysis allows to evaluate the nutritional status and the balance of body fluids compartments.