eGFR blood test: what estimated glomerular filtration rate measures, normal levels by age, CKD stages, and what a low eGFR means

The glomeruli are the roughly two million microscopic filters in the kidneys, and the glomerular filtration rate is the volume of blood they clear each minute. Measuring it directly is laborious, so laboratories estimate it from the blood creatinine, a waste product of muscle that the kidneys remove at a steady rate, together with age and sex, using the CKD-EPI equation; since 2021 the recommended version no longer includes a race term. The result is scaled to a standard body surface area of 1.73 square meters so that people of different sizes can be compared.

eGFR is only as good as the creatinine it is built on. Anything that raises creatinine without the kidneys changing lowers the estimate: high muscle mass, creatine supplements, a large meat meal, dehydration and some medications that block creatinine secretion. Anything that lowers creatinine raises the estimate: low muscle mass, amputation, liver disease, pregnancy and a vegetarian diet. For those situations, cystatin C, a protein produced by all cells at a rate independent of muscle, provides a second estimate, and laboratories can report an eGFR from creatinine and cystatin C combined, which is the most accurate routine option.

Because eGFR describes filtration alone, kidney health is judged together with the urine albumin-to-creatinine ratio, which detects damage to the filters before filtration falls. The two together stage kidney disease and predict its course far better than either alone.

eGFR is reported automatically with the creatinine on every basic and comprehensive metabolic panel, so most adults have it checked yearly. It is monitored deliberately in people with diabetes and high blood pressure, the two most common causes of kidney disease; in known chronic kidney disease at a frequency set by the stage; in heart failure; in people taking medications that affect the kidney or are cleared by it, including NSAIDs, metformin, lithium, some antibiotics and antivirals and contrast dye; in anyone with a family history of kidney disease; and in people using creatine or high-protein diets, in whom a low estimate needs a cystatin C check before it is believed.

Kidney disease is silent until it is advanced. Most people with an eGFR of 45 to 60 feel nothing, and the point of routine testing is to find and slow it while that is still true.

eGFR comes with the basic metabolic panel, the comprehensive metabolic panel and the renal panel, any of which your doctor can order or you can order online through TestWell for a draw at a Quest or Labcorp patient service center. A licensed physician reviews the order, and results post to your portal within one to three business days with creatinine and eGFR against their ranges. Add cystatin C to the same draw if you have high muscle mass, use creatine, or want the most accurate estimate, and add a urine albumin-to-creatinine ratio to complete the kidney picture.

Fasting is required for the glucose on a metabolic panel. Drink normally in the days before; dehydration lowers eGFR. Avoid a large meat meal the evening before and hard exercise for 24 to 48 hours, both of which raise creatinine. Skip NSAIDs such as ibuprofen and naproxen for a few days beforehand if your prescriber agrees, and tell the ordering physician about creatine, protein supplements, and every medication.

An eGFR of 90 or more is normal for a healthy adult. Filtration declines slowly with age, by roughly one milliliter per minute per year after about 40, so a healthy 75-year-old commonly has an eGFR in the 60s or 70s without disease, and a value that would prompt concern in a 30-year-old is expected in an 80-year-old. Laboratories often report values above 60 simply as greater than 60 or with the calculated number, and many use 60 to 120 as the reference band.

Chronic kidney disease is staged by eGFR sustained for at least three months: stage G1 is 90 or more with evidence of kidney damage such as albumin in the urine; G2 is 60 to 89 with damage; G3a is 45 to 59; G3b is 30 to 44; G4 is 15 to 29; and G5, below 15, is kidney failure. An eGFR of 60 to 89 without urine albumin or other damage is not kidney disease. Each stage is further described by the urine albumin level, A1 (normal), A2 (moderately increased) and A3 (severely increased), because at any given eGFR more albumin means faster progression and higher cardiovascular risk.

A single eGFR below 60 has two very different explanations, and the first job is to tell them apart. The first is a creatinine that is high for reasons other than the kidney: dehydration, a creatine supplement, high muscle mass, a large protein meal, a hard workout, or a medication that interferes with creatinine handling. A repeat well hydrated, off creatine and NSAIDs, ideally with cystatin C, resolves it, and a normal cystatin C-based eGFR in that setting is reassuring. The second is genuinely reduced filtration, which is chronic kidney disease when it persists for three months and acute kidney injury when it appears over days.

Diabetes and high blood pressure cause most chronic kidney disease in adults; glomerular diseases, polycystic kidney disease, long-term NSAID use, recurrent obstruction from stones or an enlarged prostate, and inherited conditions account for the rest. Acute injury follows dehydration, severe infection, contrast dye, some antibiotics and NSAIDs, and blockage of urine flow. Symptoms appear late: fatigue, swelling, itching, nausea, changes in urination and trouble concentrating usually mean the eGFR is well below 30.

What follows a confirmed low eGFR is a urine albumin-to-creatinine ratio, a check of blood pressure and glucose or A1c, a review of medications for kidney safety and dose adjustment, and a plan for how often to retest. The measures that slow kidney disease, blood pressure and glucose control and certain medication classes, work best when started at stage G3a rather than G4, which is the whole argument for finding it early.

An eGFR well above 120 is usually a calculation effect rather than super-normal kidneys: low muscle mass, a vegetarian diet, pregnancy, liver disease and amputation all lower creatinine and inflate the estimate, and laboratories therefore often cap the reported value. Genuine hyperfiltration, in which the kidneys filter more than normal, occurs in early diabetes, in obesity and in pregnancy, and in diabetes it can precede the later decline; it is noted rather than treated, with attention to glucose and blood pressure. A high eGFR needs no follow-up on its own.

Confirm before concluding: repeat the creatinine and eGFR in two to four weeks after normal hydration, without creatine, NSAIDs, heavy meat meals or hard exercise, and add cystatin C for a muscle-independent estimate. Add a urine albumin-to-creatinine ratio, which stages the disease and predicts its course. If the low value persists, blood pressure, glucose or A1c, a urinalysis, electrolytes, and a kidney ultrasound when the cause is unclear follow, together with a review of every medication for kidney safety. Retesting frequency then follows the stage, from yearly for mild reductions to every few months for advanced disease, and a nephrology referral is standard for eGFR below about 30, rapidly falling values, or heavy albumin loss.