It is used to determine whether your kidneys are functioning normally. A combination of blood and urine creatinine levels may be used to calculate a "creatinine clearance." This measures how effectively your kidneys are filtering small molecules like creatinine out of your blood.

Creatinine may be part of a routine blood test, widely used when someone has non-specific health complaints, or when your doctor suspects kidney problems. The test is also used to monitor treatment of kidney disease or to monitor kidney function while you are on certain drugs.

Increased creatinine levels in the blood suggest diseases that affect kidney function. These can include:

• glomerulonephritis (swelling of the kidney’s blood vessels);
• pyelonephritis (pus-forming infection of the kidneys);
• acute tubular necrosis (death of cells in the kidneys’ small tubes); 
• urinary tract obstruction; or
• reduced blood flow to the kidney due to shock, dehydration, congestive heart failure, atherosclerosis, or complications of diabetes.

Creatinine can also increase as a result of muscle injury. Low levels of creatinine are not common and are not usually a cause for concern. As creatinine levels are related to the amount of muscle the person has, low levels may be a consequence of decreased muscle mass (such as in the elderly), but may also be occasionally found in advanced liver disease.

Since creatinine levels are in proportion to muscle mass, women tend to have lower levels than men.

In general, creatinine levels will stay the same if you eat a normal diet. However, eating large amounts of meat may cause short-lived increases in blood creatinine levels. Taking creatine supplements may also increase creatinine.

There are a few drugs that interfere with the creatinine test, although there are some drugs that can cause some impairment in kidney function. Your creatinine levels may be monitored if you are taking one of these drugs.