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
This test measures the amount of creatinine in your blood and/or urine. Creatinine is a waste product produced in your muscles from the breakdown of a compound called creatine. Creatine is part of the cycle that produces energy needed to contract your muscles. Both creatine and creatinine are produced by the body at a relatively constant rate. Almost all creatinine is excreted by the kidneys, so blood levels are a good measure of how well your kidneys are working. The quantity produced depends on the sex, size or age of the person and their muscle mass. For this reason, creatinine concentrations will be slightly higher in men than in women and children.
Results from a blood creatinine test and a 24-hour urine creatinine test may be used to calculate creatinine clearance.
How is the sample collected for testing?
A blood sample is taken from a vein in the arm. You may be asked to collect a complete 24-hour urine sample in addition to having your blood taken (see "Creatinine Clearance"). 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.
Is any test preparation needed to ensure the quality of the sample?
No test preparation is needed.
How is it used?
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.
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 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.
What does the test result mean?
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
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 concentration.
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.
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 all 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 requested with creatinine?
What happens to creatinine in pregnancy?
On This Site
Tests: Urea; GFR and eGFR; Creatinine Clearance; Urinalysis; Urine Albumin and Urine Albumin/Creatinine Ratio; Renal Panel; Cystatin C; Beta-2 Microglobulin
Conditions: Congestive Heart Failure, Diabetes, Kidney Disease