Creatinine Clearance (Serum-Based, 24-Hour Collection)

What Is Creatinine Clearance?

Creatinine clearance is a measure of how well your kidneys filter waste products like creatinine from your blood. Unlike a single blood test, this test requires collecting all of your urine over 24 hours to get an accurate picture of kidney function. This method helps doctors determine how effectively your kidneys are working to remove waste and maintain your body’s balance of fluids and electrolytes.

How Is This Test Performed?

You’ll need to collect every drop of urine for a full 24-hour period, starting after you’ve emptied your bladder at the beginning of the test. Your healthcare provider will provide instructions on how to properly collect your urine samples. Blood is drawn at the start and end of the collection period to measure your serum creatinine level.

Why Might Your Doctor Order This Test?

Your doctor may order creatinine clearance if they suspect kidney disease, monitor kidney function in people with chronic conditions (like diabetes or high blood pressure), or evaluate how well you’re tolerating medications that affect kidney function. It’s also useful before surgeries or procedures that could impact kidney function.

What to Expect Before the Test

No special preparation is usually needed for the blood draw, but you’ll need to collect all urine for 24 hours. Drink plenty of fluids to help your kidneys produce urine, but avoid excessive caffeine or diuretics unless instructed otherwise. Wear comfortable clothing and plan for time to collect urine at home or in a clinic.