Does the Estimated GFR Cause Us to Cry Wolf with Chronic Kidney Disease?

Abstract & Commentary

By Joseph E. Scherger, MD, MPH

Synopsis: An analysis of more than 1 million persons in Alberta, Canada, showed that laboratory reporting of estimated glomerular filtration rate (GFR) beginning in 2004 resulted in more referrals to nephrologists, but no apparent improvement in outcomes.

Source: Hemmelgarn BR, et al. Nephrology visits and health care resource use before and after reporting estimated glomerular filtration rate. JAMA 2010;303:1151-1158.

The estimated glomerular filtration rate (eGFR) came into widespread use in 2004 and is based on the serum creatinine (Cr) with minor adjustments using the patient's age, race, and gender. The eGFR is often reported along with the serum Cr in chemistry panel results.

A study group from the University of Calgary, Alberta, Canada, and the Alberta Kidney Disease Network looked at a community-based cohort of 1,135,968 persons before and after the reporting of eGFR starting in October 2004. The rate of first nephrologist visits went up substantially after the onset of eGFR reporting. Among patients with an eGFR < 30 mL/min/1.73 m2, there was a 95% increase in referrals. There was no evidence of an increase in the use of angiotensin-converting enzyme (ACE) inhibitors or angiotensin II receptor blockers (ARBs) for chronic kidney disease (CKD). The authors conclude that eGFR reporting increases the rate of first visit to a nephrologist without any apparent improvement in outcomes.

Commentary

There is a shortage of nephrologists in the United States and globally.1 An estimated 31 million Americans (16% of the population) have a form of CKD and 506,000 Americans are being treated for ESRD.2 Should the estimated 8300 nephrologists in the United States see every patient with CKD? What is the role of primary care?

According to the National Kidney Foundation, a normal GFR is between 90 and 130 mL/min (stage 1). Kidney damage with mild decrease in kidney function (stage 2) is between 60 and 90 mL/min. Moderate decrease in kidney function (stage 3) is between 30 and 60 mL/min. Severe decrease in kidney function (stage 4) is between 15 and 30 mL/min with kidney failure (stage 5) being a GFR < 15 mL/min.3

Before the addition of the eGFR, primary care physicians had been used to evaluating kidney function based on the serum BUN and Cr. Serum levels of Cr < 1.5 mg/dL have generally been considered normal or benign. The National Library of Medicine lists a normal Cr as 0.8-1.4 mg/dL.4 Yet, the eGFR for me, a 59-year-old non-African-American male, with a Cr of 1.4 would be 52 mL/min, or Stage 3 CKD! If I were age 79, my eGFR with a serum Cr of 1.4 mg/dL would be 48 mL/min. A 79-year-old male (not African-American) with a Cr of 1.2 mg/dL has an eGFR of 58 mL/min, still stage 3. The eGFR causes us to call patients previously thought of as normal as having moderate CKD.

It is understandable that most primary care physicians would refer to a nephrologist any patient with stage 3 CKD. Most of these referrals would not have been triggered by a serum Cr < 1.5 mg/dL. The eGFR has changed that and puts the number < 60 mL/min in front of us with many patients. More compulsive or conscientious physicians (based on your point of view) might refer anyone with stage 2 disease or an eGFR < 90 mL/min. This would be most people with a serum Cr ≥ 1.2 mg/dL. What would the nephrologist do with these patients? One would hope that without too many other tests, they would be counseled on the control of their hypertension and diabetes, and would be followed. Primary care physicians can do that.

There is a convenient online calculator of eGFR available from the National Kidney Foundation.5 Using the eGFR calculator, a level of 30 mL/min (severe disease) begins to occur at a serum Cr > 2 mg/dL. The limited number of nephrologists in the United States should be focusing on the care of these patients. Prevention of severe CKD and failure is the work of primary care physicians, and we should become more knowledgeable in managing patients with mild-to-moderate disease. We do this with hypertension, diabetes, and asthma. The prevention and management of CKD should become more common in our continuing education and clinical work, and the use of eGFR underscores this need. Assuming the eGFR is an accurate reflection of GFR, it may be time to rethink the classification of CKD and to put out more recognized guidelines for the management of these patients in primary care.

References

1. Field M. Addressing the global shortage of nephrologists. Nat Clin Pract Neprol 2008;4:583.

2. Bizzozero J. Understanding the nephrologist shortage: Is there a nephrologist in the house? Renal Business Today. Sept. 30, 2009. Available at: www.renalbusiness.com/articles/understanding-nephrologist-shortage.html. Accessed June 4, 2010.

3. National Kidney Foundation. Glomerular Filtration Rate (GFR). New York; 2010. Available at: www.kidney.org/kidneydisease/ckd/knowgfr.cfm. Accessed May 30, 2010.

4. Medline Plus. Creatinine — blood. National Library of Medicine, National Institutes of Health; 2009. Available at: www.nlm.nih.gov/medlineplus/ency/article/003475.htm. Accessed May 30, 2010.

5. National Kidney Foundation. Calculators for Health Care Professionals. Available at: www.kidney.org/professionals/KDOQI/gfr_calculator.cfm. New York; 2009. Accessed May 30, 2010.