Validation of the revised MDRD formula and the original Cockcroft and Gault formula for estimation of the glomerular filtration rate using Australian data.

AIMS: The estimation of glomerular filtration rate (eGFR) using the MDRD (Modification of Diet in Renal Disease) formula is a recommended practice in Australia, New Zealand and other countries. Since the original development of this formula, an international process to align assays for serum creatinine has been undertaken and a revised version of the MDRD formula has been produced for these assays. Additionally, the Cockcroft and Gault (C&G) formula remains recommended for drug dosing decisions, although there are different versions of the formula using either actual weight or calculated ideal body weight. We aimed to assess these formulae using Australian data.
METHODS: We assessed the revised MDRD and the C&G formulae by comparison with radio-isotope GFR measurements using patients routinely referred for this test. The MDRD was compared to GFR corrected for body surface area and the C&G to the uncorrected GFR.
RESULTS: The MDRD was shown to have the expected scatter of over +/-30% but with median values not significantly different from isotopic GFR measurements and without a systematic deviation due to age, gender, height, weight or body mass index (BMI). The original C&G formula generally provided a good estimate of GFR, however the use of ideal body weight rather than actual body weight produced an under-estimated GFR in this population which was more prominent with increasing age and BMI.
CONCLUSIONS: The MDRD and original C&G formulae were found to be valid in an Australian setting. The C&G formula, when calculated using weight estimated from patient height, was found to underestimate GFR in some patients.