Creatine is a compound naturally created by our body to produce the energy needed for muscle contraction. When your muscles break down creatine, a waste product called creatinine is formed. Your kidneys excrete almost all the creatinine in your blood. If your kidneys do not function properly, creatinine remains in the blood. Because of this, creatinine blood tests are often used to measure your level of kidney function.
Causes of Abnormal Creatinine
Although normal blood creatinine levels can vary between individuals, most labs define a normal creatinine level as 0.8 to 1.4 mg/dL. If a blood test shows that your creatinine levels exceed 1.4 mg/dL, it can indicate one of several conditions that affect the kidneys such as bacterial kidney function, kidney stones, inflammation of the blood vessels in the kidneys and reduced blood flow to the kidneys. Creatinine levels can also increase with acute kidney disease, chronic kidney disease and kidney failure.
Creatinine and Glomerular Filtration Rate
The amount of creatinine in your blood can also determine your glomerular filtration rate, or GFR. The GFR represents the amount of blood that passes through the filters in your kidneys, called the glomeruli, per minute. A normal glomerular filtration rate falls between 90 to 120 mL/min. If your GFR falls below 60 mL/min for a period of 3 or more months, it indicates chronic kidney disease. A GFR of less than 15 mL/min indicates kidney failure.
Urine Creatinine
Your doctor may also recommend a urine creatinine test to determine your level of kidney function. In healthy individuals, urine contains high amounts of creatinine because your kidneys remove the waste product from your blood and deposit it into your urine. A urine creatinine test usually involves collecting your own urine for an entire 24-hour period and then bringing it into your doctor for testing. A normal urine creatinine level usually falls between 500 to 2,000 mg. The exact number depends on your age and the amount of lean body mass that your body contains. If your kidneys are not functioning properly, your urine will contain low levels of creatinine because the waste product remains in your blood.
Considerations
Although your doctor can use creatinine tests to determine whether or not your kidneys are functioning properly, they cannot determine the cause of abnormal kidney function. If your doctor determines you have abnormal creatinine levels, further laboratory testing is needed to isolate the exact condition causing your reduced kidney function.
References
- MedlinePlus; Creatinine - blood; David C. Dugdale; August 7, 2009
- Lab Tests Online; Creatinine; March 22, 2011
- National Kidney Foundation: Glomerular Filtration Rate;
- MedlinePlus; Creatinine - urine; David C. Dugdale; August 7, 2009
- MedlinePlus; Glomerular Filtration Rate; Paul Patel; August 12, 2009
