Creatinine Clearance Test
What is the creatinine clearance test?
The creatinine clearance test is an older test used to check your kidney function. This test allows your healthcare provider to look at samples of your urine and blood to see how much of the waste product — creatinine — is filtered out by your kidneys. Abnormal levels of creatinine in your urine and blood could point to an issue like kidney disease.
Done in two parts, the creatinine clearance test involves collecting your urine over a 24-hour period of time and then having your blood drawn. These samples are then tested to see how much creatinine was filtered through your kidneys over the 24-hour window. The results of the test will be used in a mathematic formula that figures out your creatinine clearance. Creatinine clearance is one way to estimate your glomerular filtration rate (GFR), or how well the kidneys are filtering your blood. The GFR is the main number used by your provider to determine how well your kidneys are working.
The creatinine clearance test is not used very often any more. It has largely been replaced by the estimated GFR (eGFR) equations using creatinine levels in the blood — which means a 24-hour urine collection is not needed.
What is creatinine?
Creatinine is actually a waste product of creatine. Creatine is a chemical that your body uses to supply your muscles with energy. As you muscles use energy the tissue that makes up your muscles breaks down. This natural breakdown of muscle tissue causes creatinine to be released into your bloodstream. This is when creatine becomes creatinine.
Normally, creatinine is filtered out of your blood by your kidneys. If you think of each organ in your body as having a job, the kidneys are the filters. They’re responsible for cleaning your blood. The material that’s removed from your blood leaves your body in your urine. If your kidneys aren’t working properly, than you may have higher levels of creatinine in your blood than you should.
Why do I need to have the creatinine clearance test?
Anyone can be at risk for a kidney disease at some point in their life. However, some people have a higher risk of developing a kidney problem than others. These risks can include:
- Age (you could be at a higher risk after age 60).
- High blood pressure (hypertension).
- Family history of kidney disorders.
- Heritage (there’s a higher risk for people of an African-American, Asian, Native American or Pacific Islander background).
When is the creatinine clearance test done?
The creatinine clearance test is done when your healthcare provider thinks that the eGFR result given with your blood creatinine level may not be accurate. Examples includes when people have very little or a lot of muscle on their bodies. However, there are ways to check this, such as with the eGFR result using cystatin C, another blood test. As a result, creatinine clearance is rarely used in modern practice.
Are there any symptoms associated with a high creatinine level?
Kidney disease tends to be silent and, for many people, there are no symptoms in the early stages. However, as the disease progresses, you may experience a few symptoms. These can include:
- Fatigue (feeling tired).
- Changes in how often you urinate.
- Loss of appetite.
Why is the creatinine clearance test done?
The creatinine clearance test is to confirm the level of kidney function reported with the eGFR level. Your healthcare provider will want to know how well your kidneys are working. The results of this test can lead to a diagnosis of kidney disease.