UNREQUESTED GFR DETERMINATIONS
Our local laboratories have been adding glomerular filtration rates (GFR) to our basic metabolic panels. What should we do when the GFR indicates stage 3 chronic kidney disease but the creatinine level is normal?
—Randy Zeid, DO, Browns Mills, N.J.
In the absence of a 24-hour urine collection to calculate creatinine clearance, I’ll presume that the lab you work with is estimating GFR on the basis of either the Cockcroft-Gault equation or the Modification of Diet in Renal Disease (MDRD) equation. These equations can accurately assess GFR in patients with stable renal function who are not amputees, unusually muscular or obese, vegetarians, over the age of 70, pregnant, or of certain ethnic groups, such as of Chinese origin (Am J Kidney Dis. 2005;45:463-472). If your patients don’t fall into these subgroups, the estimated GFR can be a valuable piece of information, especially if it reveals stage 3 chronic kidney disease defined as a GFR of 30-59. Therefore, I would advise you to begin the process of identifying and treating reversible causes of renal dysfunction (hypoperfusion, obstruction, nephrotoxic drugs, etc.), begin efforts to slow progression of disease (BP control, use of ACE inhibitors if appropriate), treat the complications of renal dysfunction as they arise, and consider referral to a nephrologist.
—Daniel G. Tobin, MD (108-14)