Pros and cons of the estimated Glomerular Filtration Rate

As many as 26 million Americans live with chronic kidney disease (CKD) and according to the National Institutes of Health (NIH), at least 10.4 million (or 40%) don't even know they have it. Enter the estimated Glomerular Filtration Rate (eGFR), which has become the preferred method for identifying people with CKD.

William Bennett, MD, FASN, of Legacy Good Samaritan Hospital (Portland, OR) and Editor of ASN's Clinical Journal of the American Society of Nephrology (CJASN) recently spoke with Richard Glassock, MD, from the David Geffen School of Medicine at the University of California, Los Angeles (Los Angeles, CA) about the pros and cons of this test. The conversation will be available via podcast through ASN's website at http://asn-online.org/publications/kidneynews/podcast.aspx and available on iTunes on Tuesday, September 22 (ASN Kidney News Podcast).

eGFR is most commonly calculated using the Modification of Diet in Renal Disease (MDRD) study equation ostensibly to provide a more clinically useful measure of kidney function than serum creatinine alone. The equation takes into account several factors like age, gender, and race that impact creatinine production. Analysis of blood samples for creatinine is commonly employed to evaluate kidney function and to diagnose chronic and acute diseases of the kidney. Kidney function tends to slowly decrease with normal aging after about age 30-40 years and if this normal decline is not taken into account for older persons, mainly women, the result will be that more individuals are falsely diagnosed with kidney disease.

Dr. Glassock notes that "the introduction of the concept of eGFR by equations such as MDRD has had a dramatic increase on the awareness of CKD," but he also expresses concern that the equation "has resulted in an increase in false positive diagnoses of CKD, as well as the number of possibly unnecessary referrals to nephrologists." The interpretation of eGFR from serum creatinine values is a common occurrence in clinical practice, and physicians need to understand the potential pitfalls and inaccuracies as well as benefits in order to achieve optimum patient care.

Dr. Glassock recommends using the test to establish the severity of existing CKD but not for initial diagnosis or for qualifying living donors. In those instances, an analysis of freshly voided urine for cells, protein, and glucose should accompany a serum creatinine measurement for diagnosis of CKD, he says.

The podcast on eGFR follows the series entitled "Controversies in Nephrology" that appeared in the September 2008 issue of CJASN. ASN continues to lead the fight against kidney disease by highlighting complex areas of interest and controversy such as the appropriate use of eGFR measurements.