A new equation for estimating renal function using age, body weight and serum creatinine.
BACKGROUND
Many formulas have been developed to estimate glomerular filtration rate (GFR). The aim of our study was to propose a new, more reliable equation.


METHODS
The study considered 530 subjects (training sample) with M/F 280/250, age 57.1 +/- 17.4, creatinine clearance (CrCl) 55.2 +/- 38.2 (range 2.1-144.0) for the development the new equation. A linear model was used to describe Cr production using serum Cr (sCr), age, and body weight (BW) as variables: (CrCl + b(4)) . sCr = b(1) - (b(2) . age) + (b(3) . BW) subsequently estimating parameter values by linear least squares, with CrCl as the dependent variable, and 1/sCr, age/sCr, BW/sCr as independent variables. CrCl = {[69.4 - (0.59 . age) + (0.79 . BW)]/sCr} - 3.0 (males) and {[57.3 - (0.37 . age) + (0.51 . BW)]/sCr} - 2.9 (females). A 229-patient renal failure validation sample with M/F 166/63, age 53.0 +/- 14.8, GFR 32.0 +/- 14.3 (range 4.3-69.8), assessed using iohexol Cl, was considered to compare the Cockcroft-Gault (C-G) and MDRD formulas with the new equation for estimating GFR.


RESULTS
The mean % error in GFR estimated by the new equation (+2.3 +/- 28.3%) was better than with the C-G and MDRD formulas (+5.2 +/- 30.1% and -11.4 +/- 25.9%, respectively, p < 0.0005 and p < 0.0001), and so was the mean absolute % error, bordering on statistical significance (19.8 +/- 20.3 vs. 21.1 +/- 22.0 and 22.4 +/- 17.3, p = 0.08 and p < 0.005). The precision was also better (RMSE = 7.89 vs. 8.02 and 9.13). The Bland-Altman test showed no GFR over or underestimation trend (measured +/- predicted GFR/2 vs. % error, R2 = 0.001).


CONCLUSIONS
The new equation appears to be at least as accurate as the C-G and MDRD formulas for estimating GFR.
Virga
Giovambattista
G
Nephrology and Dialysis Unit, Camposampiero/Padova, Italy. virgolino14@libero.it
Gaspari
Flavio
F
Thomaseth
Karl
K
Cara
Marilena
M
Mastrosimone
Stefania
S
Rossi
Vittorio
V
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000375:Aging; D001835:Body Weight; D003404:Creatinine / Q000097:blood*; D005260:Female; D005919:Glomerular Filtration Rate; D006801:Humans; D016014:Linear Models; D008297:Male; D008875:Middle Aged; D008954:Models, Biological; D015203:Reproducibility of Results
D003404:Creatinine