by Jay Luxenberg, MD, FACP, AGSF and Flora Bessey Pharm.D., CGP

The October issue of the Journal of the American Geriatrics Society has a very important article by UCSF’s Janice Schwarz, MD entitled Potential Effect of Substituting Estimated Glomerular Filtration Rate for Estimated Creatinine Clearance for Dosing of Direct Oral Anticoagulants. Dr. Schwartz used data from several thousand patients to compare the use of the estimates for renal clearance using the commonly reported estimated glomerular filtration rate (eGFR) with those estimated using the Cockcroft–Gault method (CrCL-CG) which usually requires a calculation to be performed by the clinician.

Although the two methods produced estimates that were highly correlated, the dose adjustments recommended for renal insufficiency have historically been provided based on the Cockcroft–Gault method. Dr. Schwartz looked at adjustments for direct oral anticoagulant (DOAC) dosing. These drugs are increasingly commonly used in long term care patients, and there are important risks associated with failure to correctly adjust dosage based on renal insufficiency. Also, edoxaban, one of the DOACs, has less efficacy when renal function is normal. It is not indicated for individuals with non-valvular atrial fibrillation and a CrCL-CG greater than 95 mL/min. Dr. Schwartz reports on the misclassifications that occur if the eGFR reported by the laboratory is used instead of the calculated Cockcroft–Gault method. Approximately 25% of people who should have their dose reduced were missed if the incorrect method of eGFR was used.  Calculating a CRCL using Cockcroft-Gault has never been easier.  No need to carry the formula around with you, simply download the free CrCl app.  Many charting programs have the option of easily pulling up a creatinine clearance calculator in the same window.  Multiple websites offer the calculator for free. Although the National Kidney Disease Education Program (NKDEP) states that the differences between methods are unlikely to result in errors in most individuals, allowing either method to be used, their recommendations were largely based on much younger and healthier people. Dr. Schwartz’s data included elderly and nursing home patients, and is much more representative of the population we serve.  I have decided to use this paper as part of our ongoing quality improvement efforts to educate prescribers to use the calculated Cockcroft–Gault method routinely to appropriately adjust medication dosing.

Ref: Schwartz, J. B. (2016). Potential Effect of Substituting Estimated Glomerular Filtration Rate for Estimated Creatinine Clearance for Dosing of Direct Oral Anticoagulants. Journal of the American Geriatrics Society, 64(10), 1996–2002.