Creatinine

It is used to find out whether your kidneys are working 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.

Urine creatinine may also be used with a variety of other urine tests as a correction factor. Since it is produced and removed at a relatively constant rate, the amount of creatinine in urine can be compared to the amount of another substance being measured. Examples of this are when creatinine is measured with protein to calculate a urine protein/creatinine ratio (UP/CR) and when it is measured with microalbumin to calculate microalbumin/creatinine ratio (also known as albumin/creatinine ratio, ACR). These tests are used to evaluate kidney function as well as to detect other urinary tract disorders.

Serum creatinine measurements along with age, weight, and gender are used to calculate the estimated glomerular filtration rate (eGFR), which is used as a screening test to look for evidence of kidney damage.

Creatinine may be part of a routine blood test, widely used when someone has non-specific health complaints, or when your doctor suspects your kidneys are not working properly.

Some signs and symptoms of kidney dysfunction include:

• Fatigue, lack of concentration, poor appetite or trouble sleeping
• Swelling or puffiness, particularly around the eyes or in the face, wrists, abdomen, thighs or ankles
• Urine that is foamy, bloody, or coffee-coloured
• A decrease in the amount of urine
• Problems urinating, such as a burning feeling or abnormal discharge during urination, or a change in the frequency of urination, especially at night
• Mid-back pain (flank), below the ribs, near where the kidneys are located
• High blood pressure

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:

• damage to or swelling of blood vessels in the kidneys (glomerulonephritis) caused by, for example, infection or autoimmune diseases bacterial infection of the kidneys (pyelonephritis)
• death of cells in the kidneys’ small tubes (acute tubular necrosis) caused, for example, by drugs or toxins
• prostate disease, kidney stone, or other causes of urinary tract obstruction; or
• reduced blood flow to the kidney due to shock, dehydration, congestive heart failure, atherosclerosis, or complications of diabetes

Creatinine blood levels can also increase temporarily as a result of muscle injury and are generally slightly lower during pregnancy.

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.

Random urine creatinine levels have no standard reference ranges. They are usually used with other tests to reference levels of other substances measured in the urine. Some examples include the microalbuminuria test and urine protein test.

For more information on reference ranges, please read Reference Ranges and What They Mean

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.