Two methods were used to estimate renal function: the Cockcroft-Gault formula
for creatinine clearance in ml/min ((140 - age in years) x body weight in kg/(serum creatinine in umol/l x 0.81) x 0.85 if female); and Modification of Diet in Renal Disease (MDRD) formula for glomerular filtration rate (GFR) in ml/min/1.73 m2 (186.3 x (age in years (-0.203)) x serum creatinine in umol/l/(88.4(-1.154)).
Creatinine clearance, Cockcroft-Gault formula
and cystatin C: estimators of true glomerular filtration rate in the elderly?
We used the Cockcroft-Gault formula
to estimate GFR which was derived from estimation of creatinine production based on gender, age, and weight .
The mean eCCL values of all subjects calculated with the formula of Schwartz (119 [+ or -] 19 (92-236) mL/min/1.73 [m.sup.2]) was normal but mildly reduced after calculation with the Cockcroft-Gault formula
(89 [+ or -] 21 (70-174) mL/min/1.73 [m.sup.2]).
[7,20] The SA 2010 ART guidelines recommended measurement of the serum creatinine concentration before treatment initiation, at 3, 6 and 12 months after initiation and then annually, with calculation of creatinine clearance (CrCl) using the Cockcroft-Gault formula
. Tenofovir was contraindicated in patients with a CrCl <50 mL/min.
A commonly used clinical estimation of renal function is based upon serum creatinine level as a surrogate marker, applying the Cockcroft-Gault formula
. (11) Accordingly, elevated creatinine is considered a marker of renal failure in the setting of ureteral obstruction and often indicates the ability of the affected renal unit(s) to drain urine properly.
GFR was furthermore calculated using six estimating formulae, Cockcroft-Gault formula
, the modification of diet in renal disease (MDRD) equations using 4 and 6 variables [26, 27], and Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equations using creatinine alone (CKD-EPI Cr) , CysC alone (CKD-EPI CysC), or both CKD-EPI (Cr-CysC)  (Table 1).
 It is generally believed that GFR calculated by Cockcroft-Gault formula
correlates well with measured GFR when renal function is within the reference interval, but as renal function declines, it overestimates GFR because creatinine is removed not only by glomerular filtration but also by renal tubular secretion.
The substudy analysis calculated estimated glomerular filtration rates (eGFR) for patients enrolled in ARISTOTLE by three difference methods: the Cockcroft-Gault formula
, the Chronic Kidney Disease-Epidemiology Collaboration formula, and cystatin C measurement.
Renal function in older hospital patients is more accurately estimated using the cockcroft-gault formula
than the modification diet in renal disease formula.
(14) Serum creatinine values should be used to estimate GFR by the Modification of Diet in Renal Disease (MDRD) equation or the Cockcroft-Gault formula
, although recent results have indicated that the MDRD equation may be more accurate.
The Cockcroft-Gault formula
has commonly been used for bedside estimation of renal function based on the patient's age, weight, gender, and serum creatinine (sCr); the formula is provided below in two versions, one using American-favored mg/dL as the unit for sCr, and the other using the international units of micromol/L--note that the later formula employs a different constant value per gender in the numerator of the equation.