What Is Gfr On A Blood Test And Whats Normal?

Your kidneys filter about 180 liters of blood every day. The eGFR on your lab report is the number that estimates how well they are doing that job. GFR stands for glomerular filtration rate — the rate at which tiny filtering units in your kidneys, called glomeruli, clear waste from your blood. A normal eGFR is generally 90 mL/min/1.73 m² or higher in adults, though what counts as normal shifts with age. The number is an estimate, not a direct measurement, and that distinction matters more than most people realize.

What Is GFR On A Blood Test And Whats Normal?

GFR is not measured directly by a blood test. It is calculated from a substance in your blood called creatinine, along with your age, sex, and sometimes other factors. The result is reported as eGFR — the “e” stands for estimated.

Creatinine is a waste product from normal muscle activity. Healthy kidneys remove it efficiently, so blood creatinine stays in a fairly steady range. When kidney filtration drops, creatinine builds up in the blood. The eGFR formula works backward from that creatinine level to estimate filtration rate.

Here is the standard interpretation for adults:

• 90 or higher — normal kidney function (called G1)
• 60 to 89 — mildly reduced (G2)
• 45 to 59 — mildly to moderately reduced (G3a)
• 30 to 44 — moderately to severely reduced (G3b)
• 15 to 29 — severely reduced (G4)
• Below 15 — kidney failure range (G5)

These categories come from the KDIGO clinical practice guidelines, which are used internationally. But a single eGFR number does not tell the whole story. A result of 58 does not automatically mean kidney disease, and a result of 95 does not automatically mean healthy kidneys.

Why Your eGFR Number Is Not the Full Picture

An eGFR of 60 to 89 without other signs of kidney damage is common and often not a concern. The KDIGO guidelines are clear that reduced eGFR alone, without markers of kidney damage, does not meet the definition of chronic kidney disease until the number stays below 60 for three months or longer.

Markers of kidney damage include protein in the urine, blood in the urine, structural abnormalities seen on imaging, or an abnormal kidney biopsy. Without at least one of these, a mildly reduced eGFR may simply reflect normal aging or individual variation.

This is where many people get unnecessarily worried. A single eGFR of 72 in a healthy 60-year-old with no protein in the urine is usually not a sign of disease. It may be entirely expected for that person’s age.

On the other hand, a normal eGFR does not rule out kidney problems. Some types of kidney disease — particularly those affecting the filtering barrier rather than the filtration rate — can cause significant protein loss in the urine while eGFR remains normal. That is why urine testing is a standard part of kidney evaluation.

Does Normal eGFR Change With Age?

Yes, and this is one of the most misunderstood aspects of eGFR. Kidney filtration rate naturally declines with age in most people. Research published in the New England Journal of Medicine and other major journals has consistently shown that GFR decreases by roughly 0.5 to 1 mL/min per year after age 40 in many healthy adults.

That means an eGFR of 75 might be perfectly normal for an 80-year-old but potentially concerning in a 30-year-old.

The eGFR formula accounts for age to some degree. It was developed using population data and adjusts the calculation based on how old you are. But the formula cannot distinguish between normal age-related decline and disease-related decline in every case.

This is why clinicians look at the trend over time, not just one number. A stable eGFR of 65 over five years tells a very different story than an eGFR that dropped from 95 to 65 in six months.

What Causes eGFR to Be Low?

A reduced eGFR can come from many sources. Some are reversible. Others are not.

The most common causes of chronic kidney disease in the United States are diabetes and high blood pressure. Both damage the small blood vessels in the kidneys over time, reducing their filtering ability. Together they account for the majority of kidney failure cases.

Other causes include:

• Glomerulonephritis — inflammation of the filtering units
• Polycystic kidney disease — a genetic condition causing cysts to grow in the kidneys
• Repeated kidney infections or urinary blockages
• Certain medications, especially long-term use of NSAIDs like ibuprofen or naproxen
• Dehydration, which can temporarily lower eGFR
• Heart failure or liver disease, which can reduce blood flow to the kidneys

Some of these are reversible. Dehydration-related drops in eGFR typically correct once you are properly hydrated. Medication-related reductions may improve if the offending drug is stopped early enough — but this depends on the specific drug and how long it was used. Some kidney damage from medications is permanent.

Age-related decline is not reversible, but it also is not necessarily progressive to the point of kidney failure. Many people with mildly reduced eGFR live normal lifespans without ever developing end-stage kidney disease.

What Happens If Your eGFR Is Below Normal?

The first step is usually a repeat test. Single eGFR readings can be affected by hydration, recent illness, diet, and even how long the blood sample sat before processing. A second test confirms whether the result is real and persistent.

If eGFR remains reduced, your doctor will likely order a urine albumin-to-creatinine ratio (UACR). This test checks for protein leaking into the urine. Protein in the urine is one of the earliest signs of kidney damage and often appears before eGFR drops.

Additional testing may include kidney ultrasound, blood tests for other markers, and a review of all medications you take. Some drugs need dose adjustments when kidney function is reduced. Others may need to be stopped entirely.

Treatment depends on the cause. For diabetes-related kidney disease, controlling blood sugar and blood pressure is the foundation. Certain blood pressure medications — particularly ACE inhibitors and ARBs — have been shown in multiple large trials to slow kidney disease progression, especially when protein is present in the urine. Newer medication classes, including SGLT2 inhibitors, have also demonstrated kidney-protective effects in people with and without diabetes.

Dietary changes may be recommended. Reducing sodium intake helps control blood pressure. In more advanced kidney disease, limiting phosphorus, potassium, and sometimes protein may be necessary. These restrictions should be guided by a doctor or kidney dietitian, not self-prescribed.

How Accurate Is eGFR?

eGFR is a good screening tool but not a perfect one. The creatinine-based formulas have limitations.

Creatinine production depends on muscle mass. People with more muscle tend to have higher creatinine levels and therefore lower calculated eGFR, even when their kidneys work fine. People with less muscle — older adults, those with muscle-wasting conditions, or people who are very thin — may have lower creatinine levels and a higher calculated eGFR that overestimates their actual kidney function.

This is a known limitation. In some cases, a 24-hour urine collection or a direct GFR measurement using a special tracer can provide a more accurate picture. These are not routine but may be used when the eGFR result does not match the clinical picture.

Newer formulas that do not rely on race have been adopted in recent years. Previous equations included a race coefficient that adjusted eGFR upward for Black patients. This practice was widely criticized because race is a social category, not a biological one, and the adjustment may have delayed diagnosis and treatment in Black patients. Most major laboratories and health systems in the US now use race-free equations.

When Should You Be Concerned?

An eGFR below 60 on two separate tests at least three months apart, with or without other signs of kidney damage, meets the criteria for chronic kidney disease. An eGFR below 45 warrants closer monitoring and likely referral to a kidney specialist. An eGFR below 30 means kidney function is significantly reduced and complications become more likely.

Symptoms of advanced kidney disease include fatigue, swelling in the legs and ankles, shortness of breath, nausea, and changes in urination. But early kidney disease often causes no symptoms at all. That is why blood and urine testing matter — they catch problems before you feel them.

If your eGFR is mildly reduced but stable, your urine shows no protein, and you have no other risk factors, the likelihood of progressing to kidney failure is low. If your eGFR is dropping over time, if protein is present in your urine, or if you have diabetes or uncontrolled high blood pressure, the risk is higher and deserves attention.

Talk to your doctor about what your specific number means for you. A single value without context can be misleading in either direction.