Estimation of creatinine clearance with a new bedside equation using age, body weight and serum creatinine
Giovambattista Virga1, Karl Thomaseth2, Marilena Cara1, Stefania Mastrosimone1, Adriana Caberlotto1, Vittorio Rossi3, Antonio Bonadonna1.
1Nephrology and Dialysis Unit, Provincial Hospital, Camposampiero (Padova), Italy
2Institute of Systems Science and Biomedical Engineering, LADSEB-CNR, Padova, Italy.
3Laboratory, Provincial Hospital, Camposampiero (Padova), Italy
virgolino14@libero.it
Glomerular filtration rate is usually estimated by calculating creatinine clearance (CrCL). Bedside formulas have been developed to estimate CrCL using age, body weight (BW) and serum creatinine (sCr). The most widely used is the Cockcroft and Gault (C-G) formula: CrCL (mL/min)= [(140-age)*BW] / (72*sCr) for males, multiplied by 0.85 for females. The aim of our study was to propose a new, more accurate equation.
The study involved 250 males and 250 females, 25-85 years old.
Our new formula is: CrCL= 79.0-[0.80*(age-BW)] / sCr for males and CrCL= 64.8-[0.44*(age-BW)] / sCr for females.
The recalculated C-G formula (recC-G), CrCL= [(a1-age)*BW] / (a2*sCr), where a1= 184 and a2= 106 for males and a1= 171 and a2= 112 for females, was used instead of the original C-G formula for a fairer comparison with the new formula.
Linear correlation analysis (estimated vs. measured CrCL) showed that the new equation was slightly more precise for males (r= 0.953 vs. 0.947) and significantly so for females (r= 0.934 vs. 0.905), while the Root Square Mean Error was a little lower (-5.0%) for males (13.88 vs. 14.61) and substantially lower (-16.3%) for females (15.46 vs. 18.47). The progressively rising error with increasing BW given by the recC-G formula both for males (R2= 0.06, p<0.0001) and for females (R2= 0.18, p<0.0001) does not emerge when the new equation is used (R2= 0.00 and 0.00 respectively, p=NS).
By comparison with the C-G, our new equation demonstrated an important improvement in accuracy when estimating CrCL especially in females.
Key Words: body weight, Cockcroft-Gault formula, creatinine clearance, creatinine excretion, glomerular filtration rate, renal function, serum creatinine.
