Also known as: Crea
Name: Creatinine
Related tests: BUN, Creatinine clearance, eGFR, CMP, BMP
Why is the test done?
To assess whether the kidneys are working normally and to monitor treatment for kidney disease.
When is it done?
Routinely as part of a basic metabolic panel; if the doctor suspects kidney dysfunction, or if you have an acute or chronic illness that could damage the kidneys and/or be made worse by kidney dysfunction; at intervals to monitor treatment for kidney disease, or kidney function while taking certain medicines.
What samples are required?
A blood sample from a vein in the arm and possibly a 24-hour urine sample.
What is being tested?
This test measures the amount of creatinine in the blood and/or urine. Creatinine is a waste product generated in the muscles by the breakdown of a compound called creatine. Creatine is part of a cycle that produces the energy needed for muscle contraction, and both creatine and creatinine are produced at a relatively constant rate. Almost all creatinine is excreted by the kidneys, so blood levels are a good indicator of how well the kidneys are working. The amount produced depends on a person’s size and muscle mass. For this reason creatinine concentrations are somewhat higher in men than in women and children.
How is the sample collected for testing?
A blood sample is taken from a vein in the arm. You may also be asked to collect a 24-hour urine sample to compare with the blood result. The doctor or laboratory will give you a container and instructions for collecting the sample properly.
Usually you start the urine collection after getting up in the morning: empty your bladder, then collect all your urine until the same time the next day.
How is it used?
When is it requested?
What does the test result mean?
Is there anything else I should know?
How is it used?
The blood creatinine test is normally requested together with the BUN (blood urea nitrogen) test to assess kidney function. Both are often requested as part of a basic or comprehensive metabolic panel (BMP or CMP), groups of tests carried out to assess the function of the body’s major organs. The BMP or CMP tests are requested for healthy people during routine check-ups and for patients with acute or chronic illness in A&E and/or hospital. If the creatinine and BUN tests are abnormal, or if the patient has an underlying disease known to affect the kidneys, such as diabetes, these two tests may be used to monitor the progression of kidney dysfunction and the effectiveness of treatment. Blood creatinine and BUN tests may also be requested to assess kidney function before other procedures, such as a CT (computed tomography) scan, that may require medicines that can damage the kidneys.
A combination of blood and urine creatinine levels can be used to calculate creatinine clearance, which assesses how well the kidneys are filtering small molecules such as creatinine from the blood. Urine creatinine can also be used with a variety of other urine tests as a kind of correction factor. Since it is produced and removed in relatively constant amounts, the amount of creatinine in urine can be compared with the amount of other substances (such as protein) being measured.
Serum creatinine measurements (together with age, weight and sex) are used to calculate the estimated glomerular filtration rate (eGFR), which is used as a screening test to assess the extent of kidney damage.
When is it requested?
Creatinine may be requested routinely as part of a comprehensive or metabolic panel, when a person has no particular complaints, has an acute illness, and/or when a doctor suspects kidney dysfunction. The blood creatinine test may be requested, together with the BUN test, at regular intervals when the patient has known kidney disease or a disease that affects kidney function or could be made worse by kidney dysfunction. Both may be requested when a CT scan is ordered, before and during certain drug treatments, and before and after dialysis to monitor the effectiveness of treatment.
What does the test result mean?
Raised blood creatinine levels indicate diseases or conditions that affect kidney function. These may include:
damage to or swelling of the blood vessels in the kidneys (glomerulonephritis) caused, for example, by infections or autoimmune diseases;
bacterial infections of the kidneys (pyelonephritis)
death of the cells in the small tubules of the kidneys (acute tubular necrosis) caused, for example, by medicines or toxins;
prostate disease, kidney stones or other causes of urinary tract obstruction; or
reduced blood supply to the kidneys due to shock, dehydration, heart failure, atherosclerosis or complications of diabetes.
Creatinine can also rise temporarily as a result of muscle damage.
Low creatinine levels are not common and are not normally a cause for concern. They may be seen in conditions that reduce muscle mass.
Creatinine levels are usually slightly lower during pregnancy.
Is there anything else I should know?
Medicines such as aminoglycosides (gentamicin) can damage the kidneys, so creatinine is monitored. Other medicines, such as cephalosporins (cefoxitin), may raise the creatinine concentration without reflecting any damage
1. Does exercise change my creatinine levels?
2. How does diet change creatinine levels?
3. What is creatine? If I take creatine, will my creatinine levels rise?
4. Do creatinine levels change with age?
5. What is the BUN/creatinine ratio?
1. Does exercise change my creatinine levels?
In general, moderate exercise does not change creatinine levels. As exercise and muscle mass increase, creatinine levels may rise slowly, but not to abnormal levels.
2. How does diet change creatinine levels?
In general, creatinine levels do not change with a normal diet. Creatinine levels may be 10-30% higher in people who eat a lot of meat.
3. What is creatine? If I take creatine, will my creatinine levels rise?
Creatine is a compound made mainly by the liver and then carried to the muscles, where it is used as a source of energy for muscle activity. Once in the muscles, some creatine spontaneously turns into creatinine. The amount of creatine and creatinine depends on muscle mass, so men have higher levels than women. Creatine is now available as a dietary supplement. If you take creatine, your creatinine levels may be higher than they would be without supplements. You should tell your doctor about all the dietary supplements you are taking to help them understand your laboratory results.
4. Do creatinine levels change with age?
Creatinine levels are related to muscle mass and kidney function. With age, muscle mass decreases, but the kidneys also tend to work less efficiently. The overall result is that blood creatinine levels do not change much with age.
5. What is the BUN/creatinine ratio?
Occasionally the doctor will look at the ratio of a person’s BUN to blood creatinine to understand what is causing higher than normal concentrations. The BUN/creatinine ratio is normally between 10:1 and 20:1. A higher ratio may be due to a condition that reduces blood flow to the kidneys, such as heart failure or dehydration. It may also be linked to increased protein, from bleeding in the gut or increased dietary protein. The ratio may be reduced with liver disease (due to reduced urea formation) and malnutrition.