Glomerular Filtration Rate (GFR) with 24-Hour Creatinine Clearance (Serum Creatinine and Urine Creatinine Ratio)

Your doctor may order this blood test to check how well your body is working, screen for certain health conditions, or monitor a treatment you are already receiving. The results help your care team make informed decisions about your health and next steps.

Your doctor may order this test if you have symptoms of kidney problems, such as swelling, frequent urination, or fatigue. It’s also used to monitor kidney function in people with diabetes, high blood pressure, or other conditions that can affect kidneys. Sometimes, it’s part of routine check-ups for those at higher risk of kidney disease.

During this test, a small sample of your blood is drawn, usually from a vein in your arm, and sent to a laboratory. Trained technicians analyze the sample and measure the levels of different substances that reflect how your organs and systems are functioning.

Blood and urine samples are collected to measure creatinine levels. Blood creatinine indicates how well your kidneys filter waste, while urine creatinine helps calculate how much waste is excreted over 24 hours. Together, these measurements estimate your glomerular filtration rate (GFR), a key measure of kidney function.

Before your test, your provider will tell you whether you need to fast or temporarily stop taking certain medicines. Drink plenty of water unless instructed otherwise, and wear a shirt with sleeves that can be rolled up easily so the blood draw site is accessible.

No special preparation is needed for this test. You may be asked to collect a 24-hour urine sample at home, but your doctor will guide you through the process. Drink plenty of water to support kidney function during testing.

A trained staff member will wrap a band around your upper arm, clean the site with an antiseptic, and insert a thin needle to collect a small tube of blood. You may feel a quick pinch or slight pressure, and the entire process usually takes only a few minutes.

Blood is drawn from a vein, usually in your arm, and urine is collected over 24 hours. The blood test is quick, while the urine collection requires consistency in timing and sample collection. Results are analyzed to determine kidney function.