Learn About eGFR and Kidney Function Basics

What Is eGFR and Why It Matters for Your Kidneys

eGFR stands for estimated Glomerular Filtration Rate. This is a number that measures how well your kidneys are filtering waste from your blood. The kidneys are bean-shaped organs that remove extra water and waste products from your blood to create urine. When your kidneys work properly, they filter about 120 to 150 quarts of blood daily to produce roughly 1 to 2 quarts of urine.

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Your eGFR score tells doctors how many milliliters of waste your kidneys filter per minute per 1.73 square meters of body surface area. This measurement is written as mL/min/1.73m². A normal eGFR is 90 or higher. If your eGFR drops below 90, it may mean your kidneys are not filtering as well as they should. The lower the number, the less filtering your kidneys are doing.

Doctors use eGFR to track kidney function because it is more accurate than other methods of measuring kidney health. The kidneys filter waste through tiny structures called nephrons. Each kidney contains about one million nephrons. When kidney disease develops, these nephrons gradually stop working. An eGFR test helps catch this problem early.

Understanding your eGFR matters because chronic kidney disease affects about 37 million Americans, according to the National Kidney Foundation. Many people do not know they have kidney disease until it is advanced because early stages often have no symptoms. Your eGFR number helps your doctor determine what stage of kidney disease you may have and what steps to take next.

Practical Takeaway: eGFR is a single number that shows how efficiently your kidneys filter waste. If you have been told your eGFR is low, understanding what this means and how it relates to kidney stages can help you make informed decisions about your health with your doctor.

How eGFR Is Calculated and What Your Results Mean

eGFR is not measured directly. Instead, doctors calculate it using a blood test that measures creatinine levels. Creatinine is a waste product your muscles produce naturally. Your kidneys filter creatinine out of your blood, so the amount of creatinine in your blood shows how well your kidneys work. Doctors also consider your age, sex, and race when calculating eGFR using specific formulas.

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The most common formula used is called the CKD-EPI (Chronic Kidney Disease Epidemiology Collaboration) equation. This formula was updated in 2021 to be more accurate for all races and ethnicities. Previously, older formulas included a race correction that many experts said was inaccurate and could delay diagnosis and treatment for Black patients. The newer formula provides more reliable results for everyone.

Your eGFR results fall into five categories that represent different stages of kidney disease:

• Stage 1: eGFR of 90 or higher — Your kidneys are working normally, but you may have signs of kidney damage like protein in your urine
• Stage 2: eGFR of 60 to 89 — You have mild loss of kidney function
• Stage 3a: eGFR of 45 to 59 — You have mild to moderate loss of kidney function
• Stage 3b: eGFR of 30 to 44 — You have moderate to severe loss of kidney function
• Stage 4: eGFR of 15 to 29 — You have severe loss of kidney function
• Stage 5: eGFR below 15 — Your kidneys are failing and you need dialysis or a kidney transplant

It is important to note that a single eGFR result does not always diagnose kidney disease. Your doctor will look at multiple results over time to see if your kidney function is staying the same, getting better, or getting worse. A one-time low result could be due to illness, dehydration, or other temporary factors. Your doctor may repeat the test to confirm the results.

Practical Takeaway: Your eGFR number places you into one of five kidney disease stages. Understanding which stage applies to you helps you and your doctor plan appropriate monitoring and treatment. A single low result does not mean you have permanent kidney disease, which is why doctors track eGFR over time.

Common Causes of Low eGFR and Kidney Function Loss

Many conditions can cause eGFR to drop and kidney function to decline. Diabetes is the leading cause of kidney disease in the United States. High blood sugar over many years damages the blood vessels in the kidneys. About one in four people with diabetes develops chronic kidney disease. This is why people with diabetes need regular eGFR testing to catch kidney problems early.

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High blood pressure is the second leading cause of kidney disease. Blood pressure is the force of blood pushing against artery walls. When blood pressure stays high for years, it damages the delicate blood vessels in the kidneys. Over time, these damaged vessels cannot filter blood properly. Controlling blood pressure through medication and lifestyle changes can slow kidney damage.

Other common causes of kidney disease and low eGFR include:

• Glomerulonephritis — inflammation of the tiny filtering units in the kidneys
• Polycystic kidney disease — an inherited condition where cysts grow in the kidneys
• Lupus and other autoimmune diseases — where the immune system attacks kidney tissues
• Recurrent kidney stones — which can damage kidney tissue if they happen frequently
• Urinary tract obstructions — blockages that prevent urine from flowing properly
• Chronic use of certain medications — like NSAIDs (non-steroidal anti-inflammatory drugs)
• Repeated urinary tract infections
• Obesity — which puts extra strain on the kidneys
• Smoking — which damages blood vessels throughout the body, including in the kidneys

Some people are born with only one kidney or with kidney abnormalities. Others may have had kidney injuries from accidents or infections. Age also plays a role. As people get older, eGFR naturally declines slightly. However, a significant drop in eGFR at any age should be discussed with a doctor.

Practical Takeaway: Diabetes and high blood pressure are the main causes of kidney disease, but many other conditions and factors can lower eGFR. Identifying the cause of your kidney function loss is important because different causes may need different treatments and management strategies.

The Connection Between eGFR and Daily Kidney Function

Understanding what your eGFR number means in practical terms can help you see how kidney function relates to your body's daily needs. When your eGFR is 90 or higher, your kidneys filter waste efficiently. You can eat most foods without special restrictions, and your body manages salt and fluid balance well. Your kidneys filter out extra potassium, phosphorus, and other minerals that your body does not need.

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As eGFR drops into Stage 3 (45 to 59), your kidneys begin to struggle with certain tasks. You may need to limit potassium-rich foods like bananas, oranges, and tomatoes because your kidneys cannot remove excess potassium as easily. Potassium helps your heart beat properly, but too much can cause dangerous heart rhythms. Similarly, phosphorus buildup can weaken your bones. Your doctor may recommend limiting foods high in phosphorus, such as dairy products and processed meats.

In Stage 4 (eGFR 15 to 29), kidney function declines significantly. Your kidneys may struggle to remove extra fluid, which can cause swelling in your legs, feet, and around your eyes. You may need to limit how much you drink. Your kidneys may also stop producing enough erythropoietin, a hormone that tells your body to make red blood cells. Without enough red blood cells, you develop anemia, which causes fatigue and shortness of breath.

By Stage 5