Biomarkers of Kidney Function: Estimated Glomerular Filtration Rate (eGFR)

Optimal Takeaways

The estimated glomerular filtration rate (eGFR) is a calculation of how well the kidneys are able to filter out creatinine, a byproduct of muscle metabolism. The eGFR equation most commonly used includes age, gender, and creatinine. A declining eGFR over time suggests compromised kidney function and should be monitored and addressed. A decreased eGFR can be seen with dehydration, kidney disease, diabetic nephropathy, cirrhosis, CHF, shock, and aging. Higher eGFR is seen with pregnancy, exercise, and high cardiac output.

Standard Range: 60.00 – 160.00 mL/min/1.73m2

The ODX Range: 90.00 – 120.00 mL/min/1.73m2

Low eGFR is associated with impaired kidney function, renal artery atherosclerosis, primary kidney disease, glomerulonephritis, acute tubular necrosis, cirrhosis with ascites, congestive heart failure, shock, dehydration, aging (Pagana 2021), and diabetic nephropathy (Nojima 2017)

High eGFR may be seen with pregnancy, exercise, and high cardiac output syndromes (Pagana 2021).

Overview

The glomerular filtration rate (GFR) reflects how well the kidneys are filtering toxins such as creatinine out of the blood. It is based on how many milliliters of fluid the nephron can filter in one minute. The GFR can be measured using creatinine clearance. This method requires a serum creatinine and a 24-hour urine sample, a process that is expensive and time consuming. Instead, estimated GFR (eGFR) is used clinically to assess renal function as well as guide medication dosing in renal insufficiency. The equation most commonly used for eGFR uses creatinine, age, and gender. The eGFR may decrease in overt kidney disease (e.g., glomerulonephritis and acute tubular necrosis) or in conditions that reduce blood flow to the kidney such as renal artery atherosclerosis, shock, and dehydration. The eGFR may not be accurate in those with malnutrition, obesity, paralysis, or pregnancy (Pagana 2021). Kidney function can also be evaluated using cystatin C for those with significantly variability in muscle mass, a factor that may influence creatinine levels (Miller 2018).

An eGFR of 90 or above is considered normal, 60-89 is mildly decreased, 45-59 mild to moderately decreased, 30-44 moderately to severely decreased, 15-29 severely decreased, and below 15 is considered stage 5 kidney failure, an indicator for dialysis or transplant. The leading cause of chronic kidney disease is diabetes followed by high blood pressure and glomerulonephritis (Raymond 2021).

Monitoring eGFR is especially important in those taking potentially nephrotoxic drugs. These include nonsteroidal anti-inflammatories (NSAIDS) which can triple the negative impact on kidney function compared to other drugs. In a prospective observational study of 270 subjects aged 60 and older, each additional drug added to a medication regimen (polypharmacy) had an independent negative impact on kidney function. Researchers note that NSAID use should be discouraged in most older individuals due to their association with increased renal, gastrointestinal, and cardiovascular risks (Ernst 2020).

Diabetic nephropathy is the leading cause of end-stage renal disease and eGFR should be monitored closely in all diabetics as optimal glucose control can slow kidney function decline. A retrospective cohort study of 2,533 type 2 diabetics with a baseline eGFR of 60 or above found that a decline in eGFR by 7.5% or more in one year or 15% or more in two years would be more likely to be associated with poor renal prognosis (Nojima 2017).

Aging can affect eGFR which is expected to decline as age advances. It is important to explore declines in eGFR further, i.e., assess for the presence of proteinuria, especially in the elderly to avoid an inaccurate diagnosis of kidney dysfunction (Glassock 2009).

References

Ernst, Rahel et al. “Polypharmacy and Kidney Function in Community-Dwelling Adults Age 60 Years and Older: A Prospective Observational Study.” Journal of the American Medical Directors Association vol. 21,2 (2020): 254-259.e1. doi:10.1016/j.jamda.2019.07.007

Glassock, Richard J, and Christopher Winearls. “Ageing and the glomerular filtration rate: truths and consequences.” Transactions of the American Clinical and Climatological Association vol. 120 (2009): 419-28.

Miller, W Greg, and Graham R D Jones. “Estimated Glomerular Filtration Rate; Laboratory Implementation and Current Global Status.” Advances in chronic kidney disease vol. 25,1 (2018): 7-13. doi:10.1053/j.ackd.2017.09.013

Nojima, Jun et al. “One-year eGFR decline rate is a good predictor of prognosis of renal failure in patients with type 2 diabetes.” Proceedings of the Japan Academy. Series B, Physical and biological sciences vol. 93,9 (2017): 746-754. doi:10.2183/pjab.93.046

Pagana, Kathleen Deska, et al. Mosby's Diagnostic and Laboratory Test Reference. 15th ed., Mosby, 2021.

Raymond, Janice L., et al. Krause and Mahan's Food & the Nutrition Care Process. Elsevier, 2021.