The creatinine clearance test checks your kidney function by looking at the amount of creatinine in your urine and blood. Creatinine is a waste product that’s typically filtered out of your blood by your kidneys. Abnormal levels of creatinine could be a sign of kidney disease.
The creatinine clearance test is a test that checks your how well your kidneys are working. It allows your healthcare provider to see how much creatinine is in a sample of your pee (urine) and blood. The results of this test can lead to a diagnosis of kidney disease.
Creatinine is a waste product of creatine. Creatine is a chemical that your body uses to supply your muscles with energy. As your muscles use energy, they break down. This natural breakdown of muscle tissue causes creatinine to release into your bloodstream. Your kidneys typically filter creatinine. But, if your kidneys aren’t functioning correctly, you may have higher levels of creatinine in your body than you should.
The creatinine clearance test involves collecting your pee over a 24-hour period and having your blood drawn. Your provider uses these samples to see how much creatinine your kidneys filter over the 24-hour window.
The results of the test show your creatinine clearance. Creatinine clearance is one way to estimate your glomerular filtration rate (GFR), or how well your kidneys are filtering your blood. The GFR is the main number used by your provider to determine how well your kidneys are working.
Healthcare providers don’t use the creatinine clearance test as much as they once did because collecting pee over a 24-hour period is inconvenient. Instead, they usually use a blood test called the estimated glomerular filtration rate (eGFR) coupled with a urine test like urine albumin-creatinine ratio (uACR), which only involves peeing one time.
High creatinine levels most often mean you have kidney damage that prevents your kidneys from working as well as they should. If you develop kidney disease, you may not have symptoms in the early stages. But, as the disease progresses, you may experience:
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A creatinine clearance test checks samples of your pee and blood for creatinine, a waste product. When your kidney function declines, they don’t filter waste as well. This means it ends up in your blood. This is just one of many tests that healthcare providers use to check kidney function. The key difference in this test is that you collect urine for 24 hours instead of just one time.
Your provider also measures the amount of creatine in your blood using a blood sample. They use these results to come up with your GFR. Your GFR tells your provider how well your kidneys are working.
Your healthcare provider may order a creatinine clearance test when they believe results of an eGFR blood test aren’t accurate. Examples includes when people have very little or a lot of muscle mass. A bodybuilder is an example of someone who may have a lot of muscle mass.
The pee collection part of a creatinine clearance test is done at home and the blood sample part is in a lab or at your provider’s office. You’ll collect all of your pee over 24 hours at home. During this time, you can still participate in your normal daily activities. You just need to stick to a schedule for collecting your urine samples and make sure not to miss any collections (you don’t flush any urine).
The second part of the test involves having your blood drawn. Your provider will give you directions on where to go to for the blood test when you pick up your test materials. Often, you’ll drop off your urine collection when you go to get your blood drawn.
Before the creatinine clearance test, your healthcare provider will tell you what you may need to do to prepare.
Your provider will give you a container to pee in and tell you how to store it over the 24-hour period when you’re collecting it. It’s important to follow the instructions your provider gives you. Make sure you collect urine throughout the test. If you skip a few times or don’t follow the instructions, you may need to repeat the test.
Some medications could affect the test’s accuracy, so you might need to temporarily stop taking them. Only stop taking medications if your healthcare provider tells you to. Make sure to let your provider know about any medication you’re taking and that there’s a complete list of all your medications in your medical record.
In general, you can eat normally before and during the creatinine clearance test. However, your provider may tell you not to eat overnight. They may also ask you not to eat meat before the test. This could change the results because there’s higher levels of creatine in meat, which would cause your body to have higher levels of creatinine during the test.
You’ll do the creatinine clearance test over 24 hours. During this time, you’ll collect your urine each time you pee. This will give your healthcare provider a good idea of your creatinine levels throughout the entire day.
Make sure to follow the directions from your healthcare provider closely. These instructions will include details about how to store your urine sample and where you’ll take it when the test is over.
After 24 hours of collecting your pee, you’ll need to have your blood drawn. This blood sample checks for creatinine in your bloodstream. This is called serum creatinine. Your provider will use a mathematical formula that determines your creatinine clearance. This rate tells your provider just how well your kidneys are filtering waste products out of your bloodstream.
It’s very important to collect urine samples throughout the entire day for the creatinine clearance test to be accurate. If you skip one urine collection, it could affect the test results. Call your healthcare provider’s office if you miss a collection to see if you should continue the test or stop and start over the next day.
The creatinine clearance test is generally painless. The first part of the test involves normal urination over a 24-hour period of time. You might experience some discomfort from the needle when you have your blood drawn. This is a necessary part of the test and happens quickly.
Once you complete the test, you only need to wait to hear from your healthcare provider about next steps. It may take a few days to hear your results.
There aren’t many risks of a creatinine clearance test. The most common side effect of a blood test is bruising at the injection site and fainting.
If your test results show your creatinine clearance is high, it usually points to a decline in kidney function. But this isn’t always the case. Your healthcare provider usually uses the results of several different tests and considers all factors before making a kidney disease diagnosis. Abnormal results could also point to:
The creatinine clearance test is generally a reliable test. Creatinine clearance is only an estimate of GFR, and in some cases can provide a result that’s higher than what your GFR really is. In addition, there are a few reasons that the results could be high or low. These include:
It’s important to talk to your healthcare provider about your results and bring any concerns you have to their attention.
Yes, drinking water can temporarily decrease creatinine levels. For the most accurate results, you should drink water as you typically do without forcing excessive water to try to ”do better” on the test.
Creatine levels alone don’t determine if you have kidney disease. Your healthcare provider uses many tests to make a diagnosis of kidney failure. A serum creatinine test (uses blood only) can give clues to how your kidneys are working. These results typically come in milligrams per deciliter (mg/dL). Your age, muscle mass and assigned sex help determine your level. Generally, a normal creatinine level is:
Remember, your healthcare provider doesn’t rely on the results of one test. They determine your GFR and use that to determine next steps.
Creatinine clearance is part of a GFR (glomerular filtration rate). Your healthcare provider calculates GFR using results of a creatine test and a mathematical equation that takes age, assigned sex and other factors into consideration.
A note from Cleveland Clinic
A creatine clearance test helps paints a picture of your overall kidney health. It involves a 24-hour urine collection and a blood draw. Because it’s not super convenient to pee in a jug all day, your healthcare provider may suggest other tests first. Discuss any concerns you have about the test with your provider and make sure you follow the instructions carefully.
Last reviewed by a Cleveland Clinic medical professional on 11/27/2023.
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