Estimated Glomerular Filtration Rate (eGFR)

A colleague, upon checking her lab test results after an annual physical, was horrified to discover a flagged eGFR result of 57 ml/min/1.73 m2; even more so after her research indicated this result could mean she had stage 3 chronic kidney disease. She immediately called her primary care physician, who informed her that since her creatinine value hadn’t changed in more than 25 years (it had been 0.9 at 29 years of age and again at 59 years of age), he ignored the eGFR as useless. So what’s the purpose of an eGFR? If physicians are ignoring it, is it necessary and important to report it with every creatinine value?

Chronic kidney disease is an increasingly huge problem facing the American population. According to the the National Kidney Foundation (NKF) Kidney Disease Outcome Quality Initiative (KDOQI) Guidelines more than 4% of the American population suffers from stage 3 chronic kidney disease, with another 3% in stage 2 and 3% in stage 1. It’s well known that renal function decreases with age, and recent estimates suggest that roughly half the US population is over the age of 50. Although creatinine is the most commonly used marker of renal function, it is a remarkably insensitive marker of renal function loss, and new markers are just being discovered and validated. Glomerular Filtration Rate (GFR) is considered the best estimate of kidney function; however it’s not simple to measure.   eGFR is an estimated GFR, calculated from the creatinine the age, gender and race of the patient. It is a way of assisting in the early diagnosis of kidney disease. To help make this diagnosis, urine albumin is an important test to use along with eGFR. In addition, both should be abnormal for >3 months in order to make the diagnosis. Early diagnosis can help prevent progression to renal failure.

The equations for calculating eGFR have evolved and improved, from the early 6-parameter formula which came out of the Modification of Diet in Renal Disease (MDRD) study, to the most recent 4-parameter CKD-EPI formula. For adults, the CKD-EPI formula is increasingly being considered the most useful of these formulas. Formulas are also available for children, and online calculators are easy to find.

Patti Jones