What is eGFR, and why does it matter?

This kidney function test can reveal early signs of diabetes, hypertension, and heart disease—here's when to get tested and how to protect your kidneys.

WRITTEN BY

Nicola Bridges

REVIEWED BY

Richard Johnson, MD

Updated: 08/12/2025|10 min read

Your kidneys' primary job is to filter waste from your body---estimated glomerular filtration rate (eGFR) measures how well your kidneys are doing that job. This biomarker speaks volumes about your kidney function, as well as your overall health, but it is typically not tested unless your physician feels there's a concern. However, many metabolic health experts believe eGFR is just as important a marker to watch as blood glucose and cholesterol levels because the kidneys affect so many other systems in the body.

"Kidney health is a crucial, often overlooked element of aging and metabolic health," says Rick Johnson, MD, FACP, emeritus professor of medicine at the University of Colorado, and founding editor of Comprehensive Clinical Nephrology. "The kidneys process and clean blood, balancing all systems to make sure they're working in a healthy way. They're the body's barometer that can indicate concern."

In this guide, we'll explain what eGFR measures, how it's calculated, what your numbers mean for your health, and how to optimize your kidney function over time.

Why care about kidney function?

The kidneys play a role in many metabolic processes. They filter about 180 liters of blood daily through about a million nephron filtering units. Each nephron consists of a bundle of capillaries (blood vessels) forming a filter called a glomerulus, and a tiny tube that removes waste and toxins via an average of 1.5 liters of urine daily.

Beyond waste removal, the kidneys regulate fluid and electrolyte balance, reabsorbing essential minerals like potassium, sodium, calcium, and magnesium, which are critical for nerve signaling, muscle contraction, and regulating cardiovascular health, among other functions.

The kidneys also help control red blood cell production and blood pressure, and play a role in skeletal health.

• They produce the hormone erythropoietin (EPO), which stimulates bone marrow to manufacture red blood cells.
• When blood pressure drops too low, they release the enzyme renin to help retain more sodium (and therefore water) to restore it to a normal level, and when blood pressure is high, they suppress renin.
• The kidneys convert vitamin D to its biologically active form, which enhances absorption of calcium and phosphorus, essential for bone health.

Estimated glomerular filtration rate can help identify how well your kidneys are performing this life-sustaining work.

How is eGFR calculated?

There's no single test for exact GFR (hence eGFR being an estimate). Instead, eGFR uses algorithms that most often analyze blood serum creatinine levels. A byproduct of muscle metabolism, creatinine is produced at a relatively constant rate and consistently filtered by the kidneys. When the kidneys aren't functioning properly, it builds up in the blood, so measuring creatinine reflects how well your kidneys filter waste. As part of the complex eGFR calculation, the creatinine measurement is interpreted in the context of your age, gender, weight, height, and sometimes race.

There are three commonly used eGFR formulas:

• The CKD-EPI (Chronic Kidney Disease Epidemiology Collaboration) is the most used formula. It was updated in 2021 to remove race from the algorithm after a task force formed by the National Kidney Foundation and the American Society of Nephrology argued that just having the same skin color is not a valuable equation factor. The task force also recommended combined testing of cystatin C---a protein that inhibits the breakdown of other proteins---as a more reliable way to assess kidney function.
• The CKD MRD (chronic kidney disease modification of diet in renal disease) is frequently used, but its algorithm still includes race.
• The inulin clearance test (ICT) is a more precise but still not exact measure. After an intravenous injection of inulin into the bloodstream, you give a urine sample so your provider can measure your inulin excretion. ICT is time-consuming and costly, so it's typically reserved for kidney transplant and research settings.

Understanding eGFR test results

eGFR score values are aligned with the five stages of kidney disease:

• Stage 1 (≥90): Normal or high kidney function. Depending on other health factors, may indicate mild kidney damage.
• Stage 2 (60--89): Mild decline in function. Often silent without symptoms.
• Stage 3 (30--59): Moderate decline. Some symptoms may begin to emerge.
• Stage 4 (15--29): Clear symptoms start to manifest, which together indicate a severe reduction in function.
• Stage 5 (less than 15): Kidney failure. Dialysis or transplant is usually urgently required.

A single eGFR value doesn't tell the whole story. Variability in eGFR readings is common due to hydration status, fever, and medications that impact blood flow (like ACE inhibitors and nonsteroidal anti-inflammatory drugs). Patterns and trends over time are more meaningful than one measurement alone.

When evaluating kidney function, clinicians typically consider eGFR alongside any symptoms as well as a blood urea nitrogen (BUN) test. High levels of nitrogen in your blood suggests your kidneys are not filtering correctly.

CKD symptoms considered with eGFR test results

Clear symptoms typically don't manifest until stage 4 of kidney disease. Then you may notice:

• Changes in urine color, odor, and frequency
• An increase in the number of times you urinate at night (nocturia)  (reflecting a reduced ability for the kidney to concentrate the urine)
• Chest pains
• Hypertension
• Pruritus (persistent itching)
• Shortness of breath, especially with exercise (reflecting the development of anemia)

Often there are no physical signs with moderate CKD other than hypertension. However, in those whose kidney function has deteriorated markedly (such as stage 5 CKD)   or who have developed severe hypertension, more serious signs may occur on the physical exam,. In this setting, your doctor may detect:

• Autonomic hyperreflexia (muscle twitches)
• Hypertensive retinopathy (retinal damage caused by hypertension)
• Pericardial friction rub (an abnormal sound produced by the fluid sac surrounding the heart, audible via stethoscope)
• Scratch marks, which may indicate pruritus (extremely itchy skin caused when urea and other waste products build up in the blood)
• Skin pigmentation changes
• Uremic frost (high levels of BUN in sweat crystallize into fine, white powder on the skin)

How precise are the current GFR calculating systems?

Each individual's combination of age, weight, and body composition affects the accuracy of eGFR, so it is not an exact science. Despite this, eGFR is currently the best and most reliable kidney function measure available when interpreted in combination with presenting symptoms and other biomarkers and when factoring in age, weight, and body composition.

When should you get your eGFR checked?

Healthy people should check their eGFR annually. It's sometimes part of a basic metabolic panel, so ask your doctor if your BMP includes eGFR. If any of the following apply, your healthcare provider may recommend more frequent monitoring:

• You're 50+
• You have risk factors, such as hypertension, diabetes, or a family history of kidney disease
• Your eGFR is borderline stage 2 (see below)
• Your levels are below 60
• You're on medications that affect kidney function

What declining eGFR means for health and longevity

Some decline in kidney function is natural with age. On average, we lose 1 percent of kidney function per year after the age of 40.

While the impact of age has nuanced implications, if your eGFR falls below 60, Johnson recommends seeing a nephrologist. "Even if no active disease is found, a consultation can be reassuring and informative," he explains. If your eGFR is 40 or below, make an appointment, because decline in kidney function can be silent until it's serious.

While this alone doesn't indicate kidney disease requiring treatment, eGFR monitoring warrants a closer look if you have or are at risk for:

• Diabetes: High blood glucose damages kidney blood vessels, causing filtration dysfunction and impairing insulin metabolism.
• Hypertension: This condition damages kidney blood vessels, which can further increase blood pressure.
• Obesity: Excess weight causes hyperfiltration, when the kidneys are overworked trying to satisfy the increased metabolic demands of a larger body.
• Frequent urinary tract infections: UTIs can move from the bladder to the kidneys, causing chronic inflammation that leads to kidney damage.
• Heart or coronary artery disease: Heart failure is a significant risk factor for CKD, and vice versa. When the heart fails to pump enough blood to meet the body's demand, the kidneys receive less oxygen-rich blood, and pressure builds up in the veins leading to them. Over time, this stress on the kidneys can trigger inflammation and scarring.
• Family history of kidney disease: Some kidney disease can be inherited, and sharing the same social and environmental factors may increase your risk.

The two leading causes of chronic kidney disease are diabetes and hypertension.

High blood glucose (hyperglycemia) makes the kidneys work harder by increasing filtration pressure and damaging small blood vessels in the nephrons. It also increases production of advanced glycation end products (AGE), molecules that promote inflammation. Combined, these effects impair the kidney's ability to filter waste.

Hypertension is a circular concern: High blood pressure damages blood vessels in the kidneys, causing them to struggle to rid the body of excess sodium. This leads to fluid retention and even higher blood pressure, creating a feedback loop in which hypertension causes kidney damage and kidney dysfunction worsens hypertension. Disruption of sodium regulation can also throw off electrolyte balance.

High blood glucose and high blood pressure are two components of metabolic syndrome, a cluster of five risk factors that elevate the chances of developing other diseases. (The other three factors are large waist circumference, high triglycerides, and low HDL.) It makes sense, then, that metabolic syndrome increases the risk of chronic kidney disease. 

How to optimize your eGFR

Kidney damage is largely irreversible, making prevention key. You can't effectively raise your eGFR or improve CKD if significant damage has already occurred. But Johnson says he sees patients slightly increase low eGFR values through positive lifestyle changes.

Keep your kidneys as healthy as possible and slow decline through these evidence-based strategies.

Eat a kidney-friendly diet

Eating a diet low in potassium, phosphorus, sodium, and animal fat, and high in fibrous vegetables and fruit, benefits kidney health, especially if your eGFR values are in the risk or CKD range. While many people benefit from high protein intake, those with impaired kidney function should eat it in moderation. The breakdown of animal protein results in waste products, like urea, that strain the kidneys and may accelerate damage.

These tips can help:

• High-fiber vegetables and fruits such as beets, berries, and apricots are good choices. They help improve blood pressure, glucose, and lipid levels and contain antioxidants and phytonutrients that help protect kidney cells from damage.
• Watch intake of potassium, sodium, and phosphorus (found in animal proteins, processed foods, and dairy products). The kidneys filter and excrete these electrolytes; too much or too little can tax the kidneys to work harder to restore balance. Electrolyte imbalances can also stress the heart.
• Favor fish as your protein. Rich in healthy omega-3 fatty acids, fish helps reduce inflammation and provides cardiovascular benefits.
• If you have meat, pick lean proteins such as poultry, turkey, and pork loin, and only eat them a few days a week. Over time, high-fat diets can contribute to kidney damage,
• Cook with extra-virgin olive oil. This fat has antioxidant and anti-inflammatory effects that may improve eGFR.
• Limit ultraprocessed foods like cookies, cereal, processed meats, and fried foods, which growing evidence links to accelerated kidney decline. These foods tend to be high in sodium, refined carbs and sugars, and sometimes phosphate. These nutrients can cause inflammation, high blood pressure, dyslipidemia, and insulin resistance.

Drink water throughout the day

Proper hydration provides the fluid necessary for the kidneys to excrete waste and keep electrolytes in balance. It also helps dilute minerals and salt in the kidneys, reducing the risk of kidney stones and UTIs.

Exercise regularly

Research indicates that moderate exercise, particularly aerobic, can improve eGFR and lower BMI and blood pressure in non-dialysis CKD patients. Just be wary of extreme exercise if you already have impaired function: Intense muscle breakdown (such as marathon runners experience) can trigger acute kidney injury.

Get enough sleep

Studies suggest a relationship between sleep duration and quality and chronic kidney disease. Aim for seven to eight hours every night. It can help to stick to regular wake and sleep times, get sunlight upon waking, avoid exercising an hour before bed, and keep your bedroom cool and dark.

Track other risk factors

To assess kidney function, most specialists focus on eGFR, BUN, creatinine, cystatin C, blood pressure, and urine protein levels. (Excess protein in your urine, or proteinuria, can indicate some leak of the kidneys' nephron filtering units.) The other biomarker that may be useful to look for injury to the parenchyma (kidney tissue) is a urinary NGAL test. This measures neutrophil gelatinase-associated lipocalin, a protein secreted by immune cells.

eGFR is essential for overall metabolic health

Your eGFR score is an essential health metric, not just for identifying kidney disease but for revealing broader metabolic and cardiovascular trends. Still, a single low eGFR isn't cause for concern. It's best to interpret trends over time in the context of age, weight, body composition, and any symptoms. Even if you have age-related decline, catching CKD early allows you to respond proactively.

Healthy lifestyle choices---especially diet, exercise, and blood pressure management---can slow kidney decline.

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