This test measures how well your kidneys are working and how well blood is flowing to them. Creatinine is a waste product that comes from normal muscle use and from meat protein in your diet. Healthy kidneys remove creatinine from the blood. It then passes out of your body through urine.
The creatinine clearance test usually compares the creatinine level in a 24-hour urine sample with the creatinine level in your blood. This tells your healthcare provider how well your kidneys are working. Creatinine clearance also helps your healthcare provider estimate your glomerular filtration rate (GFR). This is the amount of blood cleaned each minute by tiny filters in your kidneys called glomeruli.
You may need this test if you have symptoms that might be caused by kidney disease. Signs and symptoms include:
Pain near the kidneys
Swelling or puffiness, especially around the eyes and ankles
High blood pressure
Low amount of urine or trouble urinating
Dark or foamy urine
Blood in the urine
Pain in the midback
You may also need this test if the results of other blood or urine tests suggest that you may have a problem with your kidneys.
If you have already been diagnosed with kidney disease, your healthcare provider can use this test regularly to watch your kidney function and adjust your treatment if needed. If you have a disease that affects the kidneys, you may have this test to look for any changes in your kidney function. This includes diseases such as:
Congestive heart failure
You may also have a blood urea nitrogen (BUN) test. If your BUN level is high, it's a sign that your kidneys may not be working as they should.
You may also have other tests to see how much protein is leaking from your kidneys into your urine.
You may also have an ultrasound, computed tomography (CT) scan, or other imaging test done of your kidneys.
Test results may vary depending on your age, sex, health history, the method used for the test, and other things. Your test results may not mean you have a problem. Ask your healthcare provider what your test results mean for you.
Results are given in milliliters per minute (mL/min). The range for a normal test result depends on your age and gender. For adults younger than 40, normal levels are in these ranges:
107 to 139 mL/min or 1.78 to 2.32 mL/s (SI units) for men
87 to 107 mL/min or 1.45 to 1.78 mL/s (SI units) for women
Creatinine clearance rates go down as you age. For every decade after age 40, a normal test result is 6.5 mL/min less than the numbers above.
For newborns, the normal range is 40 to 65 mL/min.
An abnormal creatinine clearance rate may mean you have a problem with your kidneys. Or it may mean a problem somewhere else in your body is affecting blood flow to the kidneys.
This test is done with samples of blood and urine.
For the blood sample, a needle is used to draw blood from a vein in your arm or hand.
For a 24-hour urine test, you must collect all of your urine for 24 hours. Empty your bladder completely first thing in the morning without collecting it. Note the time. Then collect your urine every time you go to the bathroom over the next 24 hours.
Having a blood test with a needle has some risks. These include bleeding, infection, bruising, and feeling lightheaded. When the needle pricks your arm or hand, you may feel a slight sting or pain. Afterward, the site may be sore.
Giving a urine sample has no known risks.
The 24-hour urine sample has to be exact. This means all urine must be collected and properly stored during the test period. Otherwise the test results may not be accurate. This is a common problem with the creatinine clearance test. Many healthcare providers use a formula based on your blood creatinine levels alone to estimate the GFR.
If you are pregnant or have recently done intense exercise, such as running a marathon, your creatinine clearance rate could be higher than normal.
Certain medicines can cause creatinine clearance levels to be lower than normal. These include cimetidine, procainamide, certain antibiotics, and quinidine. Certain conditions, such as diabetes and congestive heart failure, may also affect the results.
You don't need to prepare for this test. Tell your healthcare provider about all medicines, herbs, vitamins, and supplements you are taking. This includes medicines that don't need a prescription and any illegal drugs you may use.