Creatinine is a chemical waste product produced in your body as a result of muscle metabolism. The breakdown of meat foods can also produce some creatinine in your body. Healthy kidneys remove creatinine from your blood and deposit in your urine for removal from the body. If you have renal failure, your kidneys may not recognize creatinine as a waste product and allow it to accumulate in your blood.
Physiology
Your kidneys contain filtering units called glomeruli. When your blood moves through your kidneys, the glomeruli are responsible for filtering out waste products and excess fluids from the blood and leaving important nutrients in the blood. The amount of blood that your kidneys filter every minute is referred to as the glomerular filtration rate, or GFR. Renal failure is characterized by damaged or destroyed glomeruli. If your kidneys fail, your GFR decreases. This also lowers the amount of waste products, like creatinine, that are removed from the blood.
Creatinine Blood Test
Creatinine levels are usually tested as a part of a basic metabolic panel, or BMP, or a comprehensive metabolic panel, or CMP, which are separate tests used to evaluate major organ function. In general, the normal range for creatinine in the blood is between 0.6 and 0.12 mg/dL. MayoClinic.com notes that what is considered normal may vary slightly between laboratories. If the levels of creatinine in your blood exceed 0.12 mg/dL, it can indicate renal failure.
Creatinine Clearance Test
If your creatinine blood test is high and your doctor suspects that you have renal failure, he may recommend a creatinine clearance test. During this test, you will be asked to collect a 24-hour urine sample. This means that you must collect all of the urine that you expel in a complete 24-hour period and bring it into your doctor's office for testing. Your blood will also be taken for a creatinine clearance test.
The creatinine clearance test measures the amount of creatinine that has been removed from your blood and deposited into your urine. If you have a high level of creatinine in your blood and a decreased level of creatinine in your urine, it indicates decreased kidney function.
Considerations
In addition to being used to diagnose kidney disease, the creatinine clearance test may also be used to evaluate level of kidney function in those with known kidney failure. Creatinine clearance tests can also be used to measure the effectiveness of dialysis.
