At a glance

Why get tested?

To determine if your kidneys work normally and to monitor treatment for kidney disease

When to get tested?

As part of a routine blood test if you have non-specific health complaints or if your doctor thinks that you may have kidney disease; at intervals to monitor treatment for kidney disease or kidney function while on certain medicines

Sample required?

A blood sample drawn from a vein in the arm.

What is being tested?

Creatinine is produced in your muscles when a compound called creatine spontaneously breaks down. Creatine is used in a process in body cells to produce the energy needed to contract muscles and it produces creatinine at a fairly constant rate. Almost all creatinine is excreted by the kidneys, so blood levels are a good measure of how well your kidneys are working.

How is the sample collected for testing?

A blood sample is drawn from a vein in the arm. In rare cases you may be asked to collect a complete 24-hour urine sample in addition to having your blood taken (see creatinine clearance). If this is required your doctor or the laboratory will give you a large container and instructions for properly collecting this sample. You will normally be asked to collect urine as soon as you wake up in the morning until the same time the following day.

 

The Test

How is it used?

It is used to determine whether your kidneys are functioning normally. A calculation based on the serum creatinine concentration, called the eGFR (estimate of glomerular filtration rate) measures how effectively your kidneys are filtering small molecules like creatinine out of your blood.

When is it requested?

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. Creatinine and the eGFR are also used to monitor treatment of kidney disease or to monitor kidney function while you are on certain drugs.

What does the test result mean?

Looking for reference ranges?

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

  • glomerulonephritis (swelling of the kidney's blood vessels)
  • diabetic kidney disease (the filters clog up with a proteinaceous substance)
  • pyelonephritis (pus-forming infection of the kidneys)
  • acute kidney injury (death of cells in the kidney's 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. Reduced 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.

Is there anything else I should know?

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.

Common Questions

Will exercise affect my creatinine levels?

In general, moderate exercise will not affect your creatinine levels. As you continue to exercise and build muscle mass, your creatinine levels may increase slightly, but not to abnormal levels.

How does diet affect creatinine levels?

In general, creatinine levels will not vary with a normal diet. Creatinine levels may be 10%-30% higher in people who eat a diet that is very high in meat.

What is creatine? If I take creatine, will my creatinine levels go up?

Creatine is a compound that is made primarily in the liver and then transported to your muscles where it is used as an energy source for muscle activity. Once in the muscle, some of the creatine is spontaneously converted to creatinine. The amount of both creatine and creatinine depend on muscle mass, so men usually have higher levels than women. Creatine is now available as a dietary supplement. If you take creatine, your creatinine levels may be higher than when you do not take the supplement. You should tell your doctor of all the dietary supplements you are taking to help him/her evaluate your lab results.

Do creatinine levels change with age?

Creatinine levels relate to both muscle mass and to kidney function. As you age, your muscle mass decreases but your kidneys tend to function less effectively. The net result is not much change in creatinine levels in the blood as you get older.

What other tests are commonly ordered with creatinine?

Creatinine and urea, together with the eGFR, are the primary tests used to check how well the kidneys filter waste products from your blood. Your doctor may also order electrolyte tests such as sodium and potassium, or calcium to help understand how your kidneys are functioning.

What happens to creatinine in pregnancy?

Creatinine levels are generally slightly lower in pregnancy.

Last Review Date: March 25, 2013