1. ¹Pharmacy Department, Peter MacCallum Cancer Centre, St Andrew's Place, East Melbourne 3002, Australia
2. ²Department of Pharmacy Practice, Victorian College of Pharmacy, Monash University, 381 Royal Parade, Parkville 3052, Australia
3. ³Department of Haematology and Medical Oncology, Peter MacCallum Cancer Centre, St Andrew's Place, East Melbourne 3002, Australia

Correspondence: MJ Dooley, E-mail: Michael.Dooley@petermac.org

⁴MJ Dooley's current address: Pharmacy Department, Peter MacCallum Cancer Institute, St Andrew's Place, East Melbourne, 3002, Australia

Received 18 July 2003; Revised 13 November 2003; Accepted 12 December 2003.

Abstract

To compare glomerular filtration rate measured by technetium-99m ([Tc^99m]) DTPA clearance with estimated creatinine clearance (CrCl) (Cockcroft and Gault (C&G) method) in patients with serum creatinine (Scr) levels <0.06 mmol l^-1, and determine the effect of rounding serum creatinine to 0.06 mmol l^-1. Patients with serum creatinine values <0.06 mmol l^-1 at the time of [Tc^99m] clearance determination were identified. Creatinine clearance was calculated by the C&G method using both actual and rounded Scr values. A total of 419 adults had GFR measured by technetium-99m diethyl triamine penta-acetic acid ([Tc^99m] DTPA) clearance. Out of this group, 26 patients had a serum creatinine value <0.06 mmol l^-1. The C&G estimates of renal function using actual serum creatinine resulted in an overall overestimation of 12.9% when compared to [Tc^99m] DTPA clearance. When the value of serum creatinine was rounded to 0.06 mmol l^-1, the formula underestimated renal function by -7.0%. Analysis of estimated creatinine clearance for different levels of renal function showed significant differences to [Tc^99m] DTPA clearance. Rounding up of serum creatinine to 0.06 mmol l^-1 improved the predictive ability of the C&G method for the patients with [Tc^99m] DTPA clearance 100 ml min^-1, but worsened the effect in those >100 ml min^-1. This work indicates that when bedside estimates of renal function are calculated using the C&G formula actual Scr should be used first to estimate CrCl. If the resultant CrCl is 100 ml min^-1, then the Scr should be rounded up to 0.06 mmol l^-1 and CrCl recalculated. Further assessment of this approach is warranted in a larger cohort of patients.