Older people may be diagnosed with chronic kidney disease because of their results on a routine blood test called eGFR (Estimated Glomerular Filtration Rate) that is used to screen for kidney damage. This test is important because patients with kidney disease often have no symptoms until just before the kidneys fail. However, it is normal for people to lose some kidney function with aging.
eGFRs are usually above 100 and a normal eGFR is considered to be greater than 65. A recent study showed that people 65 and older with an eGFR from 45 to 59, and spilling no extra protein in their urine, were not at increased risk for developing kidney failure or dying over the five years of follow-up, compared to people with eGFRs greater than 65 (JAMA Intern Med, Aug 30, 2021;181(10):1359-1366). Another recent study found the same results (Kidney Int, 2020;98(5):1286-1295).
What is eGFR?
eGFR is a laboratory test that is usually done whenever you get blood drawn, to check your blood creatinine level as an indicator of kidney function. Creatinine is a waste product from the protein that you eat and the normal breakdown of muscle. Creatinine passes through your kidneys from your bloodstream into your urine. Your eGFR, or estimated glomerular filtration rate, measures how effectively your kidneys filter creatinine from your blood. The lower the value, the less blood is being filtered by your kidneys. Low values can signify kidney damage.
Who is At Risk for Kidney Damage?
Risk factors for kidney damage include:
• high blood pressure
• family history of kidney failure
Kidney disease usually causes no symptoms until you have lost most of your kidney function, so you definitely should get checked if you have possible kidney symptoms such as:
• swelling of arms, legs or feet
• frequent urination
• chronic tiredness
• muscle cramps
• nausea or vomiting
• loss of appetite
A Normal Process of Aging May Be Mistaken for Kidney Disease
In 2002, the clinical practice guidelines of the National Kidney Foundation (NKF) began to recommend that eGFR tests should be used to help diagnose kidney damage. However this caused many people over 65 without obvious kidney disease to be diagnosed as being in kidney failure (JAMA Intern Med, Aug 30, 2021;181(10):1366-1368), even though they only had a normal age-related decline in kidney function. In 2012 a large study reported that eGFR predicted risk of kidney failure for all age groups (JAMA, 2012;308(22):2349-2360), but a review of their data showed that aging is associated with reduced eGFR.
An eGFR greater than 65 is considered to be normal. Most people under the age of 50 have eGFRs above 90. After age 60, eGFRs drop progressively, and after age 80 you may have an eGFR between 45 and 60 and not need to be treated for kidney failure as long as you don’t have any extra protein in your urine. An eGFR of 15 or lower can mean kidney failure.
Routine blood tests usually include the test called eGFR that measures kidney function. Most people will have a level above 90. However, eGFR normally drops as you age, and people over age 65 with eGFRs between 45 and 60 and no extra protein in their urine may not be harmed by these low values. Your doctor will probably recommend a thorough kidney evaluation to see if you need any special treatment, but the results may show that these values are normal for you.