Rounding of low serum creatinine levels and consequent impact on accuracy of bedside estimates of renal function in cancer patients

To compare glomerular filtration rate measured by technetium-99m ([Tc(99m)]) DTPA clearance with estimated creatinine clearance (CrCl) (Cockcroft and Gault (CG) method) in patients with serum creatinine (Scr) levels0.06 mmol l(-1), and determine the effect of rounding serum creatinine to 0.06 mmol l(-1). Patients with serum creatinine values0.06 mmol l(-1) at the time of [Tc(99m)] clearance determination were identified. Creatinine clearance was calculated by the CG 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 value0.06 mmol l(-1). The CG 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 CG method for the patients with [Tc(99m)] DTPA clearance/=100 ml min(-1), but worsened the effect in those100 ml min(-1). This work indicates that when bedside estimates of renal function are calculated using the CG 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.