eGFR Test: Results, Normal Range, and CKD Stages

How eGFR Is Calculated

Providers calculate an eGFR test score using a formula that combines a blood filtration marker with personal physical characteristics. A direct measured glomerular filtration rate (mGFR) injects a filtration marker into the bloodstream and tracks how fast the kidneys clear it. An mGFR is complicated and not widely available, usually reserved for specific circumstances such as extreme obesity or before a kidney donation. Healthcare providers usually use an estimate instead.

To estimate filtration rate, providers often start with a blood creatinine level. Creatinine is a waste product from normal wear and tear on muscles. When kidneys function properly, they filter creatinine out of the blood. If the kidneys are not working well, creatinine builds up in the blood. However, a creatinine number alone cannot determine filtration efficiency because each person generates different amounts of creatinine based on body size, diet, and physical activity. Providers enter age, weight, height, and sex into a GFR calculator formula to produce the final eGFR score.

An eGFR may also be calculated from cystatin C, a protein produced by many cells throughout the body. Cystatin C levels are not affected by muscle size, age, or diet, which leads some researchers to consider it a more accurate estimate. In some cases, providers evaluate both creatinine and cystatin C together in adults. A provider may choose cystatin C instead of creatinine for individuals who are younger than 18 or older than 65, individuals with high muscle mass, people with obesity, or individuals who are pregnant.

CKD Stages by eGFR

Chronic kidney disease stages classify kidney function using specific eGFR numerical ranges combined with evidence of kidney damage. The stage table printed on your laboratory report footnote outlines these standard medical categories.

According to the National Kidney Foundation (NKF), diagnosing and staging CKD requires two separate tests: an eGFR blood test and a urine albumin-creatinine ratio (uACR) test. Both tests are needed to evaluate kidney health. The tests usually need repeating over 3 months or longer to confirm lasting damage. If an eGFR stays below 60, or a uACR stays above 30, for 3 months or longer, it may be a sign of CKD. This means a lab footnote reading stage G1 normal or stage G2 mild describes your current eGFR band rather than an active disease diagnosis.

Broader reference guidance offers general thresholds for these numbers. According to the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), an eGFR of 60 or more sits in the normal range. An eGFR less than 60 may mean kidney disease. An eGFR of 15 or less indicates kidney failure, and most people below that level require dialysis or a kidney transplant. MedlinePlus notes that an eGFR between 90 and 100 indicates you probably do not have kidney disease, while 60 to 90 may reflect early-stage changes, 15 to 60 points to possible kidney disease, and below 15 indicates kidney failure.

Why One Low eGFR Is Not a Diagnosis

A single low eGFR reading does not prove that a person has chronic kidney disease. An eGFR is an estimate rather than a direct measurement, and it may not always reflect actual kidney damage. It is possible to receive an abnormal result without having damaged kidneys. Test values naturally vary with age, body size, and other health conditions.

Certain physical conditions make creatinine-based eGFR calculations unreliable. These situations include severe malnutrition, muscle wasting, advanced liver disease, and limb amputation. Because creatinine originates from muscle tissue, changes in total muscle mass skew the formula results. In these clinical circumstances, providers may use a measured mGFR to obtain an accurate assessment.

Kidney disease guidelines require clinical persistence over time. A single low value can reflect factors such as recent meat intake or certain medicines. Clinicians look for an eGFR remaining below 60 mL/min/1.73m2, or elevated urine protein markers, across a span of at least 3 months before confirming a diagnosis.

What Else Doctors Check With a Low eGFR

When an eGFR result falls below what is normal for you, healthcare providers order follow-up tests to evaluate kidney structure and function. Follow-up testing often includes a urine protein test, a microalbumin creatinine ratio test, and a blood urea nitrogen (BUN) test. Providers may also request an ultrasound or a computed tomography (CT) scan of the kidneys to check physical anatomy.

Early-stage kidney disease usually causes no physical symptoms. Because early loss of function produces no noticeable warning signs, providers rely on eGFR screening to detect changes before complications arise. In later stages of kidney disease, symptoms may appear. These symptoms can include swelling in the legs, feet, ankles, hands, or face, urinating more or less than usual, dry skin or itching, fatigue, muscle cramps, nausea, vomiting, and loss of appetite.

Testing is particularly important for individuals with established risk factors for kidney disease. These risk factors include diabetes, heart disease, smoking, obesity, being over age 60, or having a family history of kidney disease, diabetes, or high blood pressure. Monitoring your numbers alongside our blood pressure guide provides essential context, as high blood pressure is a kidney risk factor.

Preparing for the Test

Preparing for an eGFR blood test requires following specific instructions from your healthcare provider regarding food intake and routine medications. During the test, a clinician draws blood from a vein in your arm. The draw takes under five minutes and involves very little risk, causing only slight pain or mild bruising at the puncture site.

Your healthcare provider will tell you how to prepare for your blood draw. You may need to fast or avoid certain foods, such as meat, for several hours prior to the appointment. Eating foods like meat can affect the eGFR score. Certain medications can also alter test results. You should never stop taking a prescribed medicine unless your provider specifically tells you to do so.

Most individuals encounter an eGFR test during routine preventative health visits. The test is commonly ordered as part of a creatinine evaluation on a basic metabolic panel (BMP) or a comprehensive metabolic panel (CMP). Routine screening helps identify subtle shifts in kidney function long before physical symptoms develop.

What to Do With Your Result

Interpreting an eGFR test result requires reviewing your filtration score in the context of your overall medical history. As NIDDK explains, you cannot raise your GFR, but you can try to keep it from going lower. Healthcare providers use eGFR results to screen individuals without symptoms, diagnose individuals with symptoms, determine disease severity, monitor individuals undergoing CKD treatment, track medications that could harm the kidneys, and evaluate kidney health before specific medical procedures.

If your report displays a low eGFR or flags a CKD stage band, review the number alongside other markers on your panel. You can learn more about how creatinine, BUN, and filtration rates interact in our kidney function test guide, and explore our general walkthrough on interpreting your blood test results. Readers examining nutrition and kidney health can also review our guide on low carb diet kidney health. Ask your healthcare provider whether a repeat eGFR and a urine albumin-creatinine ratio test are needed to confirm the trend over 3 months.