Creatinine
Note: this site is for informational purposes only. To view test results or book a test, use the NHS app in England or contact your GP.
A creatinine test measures the level of creatinine in a blood sample and sometimes a urine sample to assess how well the kidneys are filtering waste from the body. It is used to detect, diagnose, and monitor kidney disease or reduced kidney function.
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 is taken from a vein in the arm. Spot urine or 24-hour urine sample collection is needed for the measurement of urine creatinine.
Test preparation needed?
None
What is being tested?
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.
Urine creatinine test is a measure of the amount of creatinine in urine. This test can be performed on a “spot” urine sample or a 24-hour urine collection, depending on which test is being requested by your clinician. Less commonly, 24-hour urine creatinine test may be used to calculate creatinine clearance. With the exception of few clinical scenarios, creatinine clearance test has largely been replaced by glomerular filtration rate (GFR) measurement.
Common questions
It is used to find out whether your kidneys are working normally. Results from blood creatinine test is used directly in the assessment of kidney function, or used indirectly, in calculated kidney markers. Blood creatinine measurements along with age and gender are used to calculate a marker called “estimated glomerular filtration rate” (eGFR). Estimated GFR is used as a surrogate marker for “creatinine clearance”, which is an estimation of how effectively your kidneys are filtering small molecules like creatinine out of your blood. Estimated GFR value is used as a screening and monitoring test to look for evidence of kidney damage. Blood creatinine is also imbedded in algorithms aimed to alert clinicians to rapid deterioration of kidney function “acute kidney injury” (AKI). Estimated GFR is used in the context of chronic kidney diseases, whilst AKI is used to alert your clinician to acute kidney diseases.
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.
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 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.
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.
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.
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.
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.
Creatinine and urea are the primary tests used to check how well the kidneys filter waste products from your blood. Your doctor may also request electrolyte tests such as sodium and potassium, or calcium to help understand how your kidneys are functioning.
Creatinine levels are generally slightly lower in pregnancy.