Creatinine is a chemical waste molecule that is generated from muscle metabolism. Creatinine is produced from creatine, a molecule of major importance for energy production in muscles. Approximately 2% of the body’s creatine is converted to creatinine every day. Creatinine is transported through the bloodstream to the kidneys. The kidneys filter out most of the creatinine and dispose of it in the urine.
Because the muscle mass in the body is relatively constant from day to day, the creatinine production normally remains essentially unchanged on a daily basis.
Most men with normal kidney function have approximately 0.6 to 1.2 milligrams/deciliters (mg/dL) of creatinine. Most women with normal kidney function have between 0.5 to 1.1 mg/dL of creatinine. Women usually have lower creatinine levels than men because women, on average, have less muscle than men.
Other factors that may affect the level of creatinine in the blood include body size, activity level and medications.
The kidneys maintain the blood creatinine in a normal range. Creatinine has been found to be a fairly reliable indicator of kidney function. Elevated creatinine level signifies impaired kidney function or kidney disease.
As the kidneys become impaired for any reason, the creatinine level in the blood will rise due to poor clearance of creatinine by the kidneys. Abnormally high levels of creatinine thus warn of possible malfunction or failure of the kidneys. It is for this reason that standard blood tests routinely check the amount of creatinine in the blood.
Creatinine can be tested in both the blood and in the urine. These tests can help evaluate kidney function.
Serum creatinine is a test that draws blood and sends it to a laboratory to be analyzed to find out how much creatinine is in the bloodstream.
Knowing your serum creatinine allows your doctor to calculate your creatinine level along with your age, gender and race, to determine your glomerular filtration rate (GFR). GFR is a measure of kidney function. If you know a serum creatinine level you can determine the stage of CKD using the GFR Calculator. A low GFR, just like an elevated serum creatinine, is not always evidence of kidney disease. Ask your doctor to help you interpret your results.
Creatinine clearance (Ccr or CrCl) measures how much creatinine is cleared out of the body, or how well kidneys filter waste. Creatinine clearance requires a combination of a urine test and blood test. Because the urine has to be collected over a period of 24 hours, the creatinine clearance is usually done after first evaluating the serum creatinine and calculating the GFR.
The symptoms of kidney dysfunction (renal insufficiency) vary widely.
Some people may have an incidental finding of severe kidney disease and elevated creatinine on routine blood work without having any symptoms. In others, depending on the cause of the problem, different symptoms of kidney failure may be present including:
Any condition that impairs the function of the kidneys is likely to raise the creatinine level in the blood. It is important to recognize whether the process leading to kidney dysfunction (kidney failure, azotemia) is longstanding or recent. Recent elevations may be more easily treated and reversed.
The most common causes of chronic kidney disease in adults are: