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

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 o0.06 mmol l À1 , and determine the effect of rounding serum creatinine to 0.06 mmol l À1 . Patients with serum creatinine values o0.06 mmol l À1 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 o0.06 mmol l À1 . 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 À1 , the formula underestimated renal function by À7.0%. 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 À1 improved the predictive ability of the C&G method for the patients with [Tc 99m ] DTPA clearance p100 ml min À1 , but worsened the effect in those 4100 ml min À1 . 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 p100 ml min À1, then the Scr should be rounded up to 0.06 mmol l À1 and CrCl recalculated. Further assessment of this approach is warranted in a larger cohort of patients.

The 6R’s of drug induced nephrotoxicity

“…Pharmacists often “round” Scr values to an arbitrary threshold value in older patients or those with low Scr values to account for low muscle mass. This practice is inaccurate and may lead to drug dosing errors in certain populations [13–16]. Currently, KDIGO guidelines on drug dosing advocate using either Cockcroft Gault or MDRD equation for drug dosing [17].…”

Glomerular Filtration Rate Equations Overestimate Creatinine Clearance in Older Individuals Enrolled in the Baltimore Longitudinal Study on Aging: Impact on Renal Drug Dosing

“…The National Kidney Disease Education Program (NKDEP) recently recommended that eGFR (MDRD equation) and the CG equation can be used interchangeably for the purpose of drug dosing, a recommendation that is controversial and has not been rigorously evaluated in older patients. In older individuals with very low S cr values (less than 1.0 mg/dl) and reduced muscle mass, a common practice of replacing S cr with an arbitrary value, such as 1.0 mg/dl, for use in the CG equation has been reported but not fully evaluated …”

National assessment of renal estimation for drug dosing among pharmacists

“…Although the C‐G equation has not definitively been shown to provide a better estimate of renal function than the MDRD or CKD‐EPI equations, it is used more frequently because most drug trials and the majority of drug package inserts use the C‐G equation to estimate renal function and formulate dosing recommendations . Recently, some package inserts have incorporated dosing recommendations using GFR values, and several respondents indicated that they do utilize the MDRD equation in clinical practice. This is consistent with national recommendations as the Kidney Disease: Improving Global Outcomes (KDIGO) guidelines advocate using either the MDRD or the C‐G equation for drug dosing purposes …”