Also known as:Creat; Blood Creatinine; Serum Creatinine; Urine Creatinine
Related tests:BUN; BUN/Creatinine Ratio; eGFR; Creatinine Clearance; Comprehensive Metabolic Panel; Basic Metabolic Panel; Urinalysis; Urine Protein to Creatinine Ratio; Urine Albumin and Urine Albumin/Creatinine Ratio; Renal Panel; Cystatin C; Beta-2 Microglobulin
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Why Get Tested?
To evaluate the health of your kidneys; to help diagnose kidney disease; to monitor treatment for kidney disease
When to Get Tested?
Routinely as part of a comprehensive or Basic Metabolic Panel; when your have signs and symptoms that may be due to kidney disease or damage or when you have a condition that may affect your kidneys and/or be worsened by kidney dysfunction; at intervals to monitor treatment for kidney disease or kidney function while on certain medications
A blood sample drawn from a vein in your arm and/or a 24-hour urine sample
Test Preparation Needed?
You may be instructed to fast overnight or refrain from eating cooked meat; some studies have shown that eating cooked meat prior to testing can temporarily increase the level of creatinine.
How is it used?
The creatinine blood test is used to assess kidney function. It is frequently ordered along with a BUN (blood urea nitrogen) test or as part of a basic or Comprehensive Metabolic Panel (BMP or CMP), groups of tests that are performed to evaluate the function of the body's major organs. BMP or CMP tests are used to screen healthy people during routine physical exams and to help evaluate acutely or chronically ill people in the emergency room and/or hospital. Sometimes, creatinine may be performed as part of a renal panel to evaluate kidney function.
Creatinine is a waste product produced by muscles from the breakdown of a compound called creatine. Almost all creatinine is filtered from the blood by the kidneys and released into the urine, so blood levels are usually a good indicator of how well the kidneys are working.
The kidneys are a pair of bean-shaped organs that are located at the bottom of the ribcage in the right and left sides of the back. Within them are about a million tiny blood filtering units called nephrons. In each nephron, blood is continually filtered through a microscopic cluster of looping blood vessels, called a glomerulus. The glomerulus allows the passage of water and small molecules but retains blood cells and larger molecules. Attached to each glomerulus is a tiny tube (tubule) that collects the fluid and molecules that pass through the glomerulus and then reabsorbs what can be used by the body. The remaining waste forms urine.
If the creatinine and BUN tests are found to be abnormal or if someone has an underlying disease that is known to affect the kidneys, such as diabetes or high blood pressure, then creatinine and BUN tests may be used to monitor for kidney dysfunction and the effectiveness of treatment. Blood creatinine and BUN tests may also be ordered to evaluate kidney function prior to some procedures, such as a CT (computed tomography) scan, that may require the use of drugs that can damage the kidneys.
Results from creatinine tests may be used in calculations that help assess kidney function:
- Blood creatinine measurements, along with age, weight, and sex, are used to calculate the estimated glomerular filtration rate (eGFR), which is used as a screening test to look for evidence of early kidney damage.
- Blood and urine creatinine levels may be used to calculate a Creatinine Clearance. This test measures how effectively the kidneys are filtering small molecules like creatinine out of the blood.
Urine creatinine may also be used with a variety of other urine tests as a correction factor. The concentration (or dilution) of urine varies throughout the day, with more or less liquid being released in addition to the body's waste products. Since creatinine is produced and removed at a relatively constant rate, the amount of urine creatinine can be compared to the amount of another substance being measured. This stable excretion rate is useful when evaluating both 24-hour urine samples and random urine samples. Examples include:
- Urine albumin/creatinine ratio (ACR). This more accurately determines how much albumin is escaping from the kidneys into the urine. It is used to screen people with chronic conditions, such as diabetes and high blood pressure (hypertension) that put them at an increased risk of developing kidney disease.
- Urine protein/creatinine ratio (UP/CR). This may be used to monitor a person with known kidney disease or damage or to screen people on a regular basis when they are taking a medication that may affect their kidney function.
When is it ordered?
Creatinine may be ordered routinely as part of a comprehensive or Basic Metabolic Panel during a health examination. It may be ordered when someone is acutely ill and/or when a health practitioner suspects that a person's 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-colored
- 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 creatinine blood test may be ordered, along with a BUN test and urine albumin, at regular intervals when someone has a known kidney disorder or has a disease that may affect kidney function. Both BUN and creatinine may be ordered when a CT scan is planned, prior to and during certain drug therapies, and before and after dialysis to monitor the effectiveness of treatments.
What does the test result mean?
Increased creatinine levels in the blood suggest kidney disease or other conditions 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 by, for example, drugs or toxins
- Prostate disease, kidney stone, or other causes of urinary tract obstruction
- Reduced blood flow to the kidney due to shock, dehydration, congestive heart failure, atherosclerosis, or complications of diabetes
Low blood levels of creatinine are not common, but they are also not usually a cause for concern. They can be seen with conditions that result in decreased muscle mass.
Levels of 24-hour urine creatinine are evaluated with blood levels as part of a creatinine clearance test.
Single, 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 urine albumin test and urine albumin/creatinine ratio and the urine protein test.
Is there anything else I should know?
Creatinine blood levels can also increase temporarily as a result of muscle injury and are generally slightly lower during pregnancy.
Some drugs may cause increased creatinine levels. Inform your healthcare provider of any drugs you are taking.
What is being tested?
Creatinine is a waste product produced by muscles from the breakdown of a compound called creatine. Creatinine is removed from the body by the kidneys, which filter almost all of it from the blood and release it into the urine. This test measures the amount of creatinine in the blood and/or urine.
Creatine is part of the cycle that produces energy needed to contract muscles. Both creatine and creatinine are produced by the body at a relatively constant rate. Since almost all creatinine is filtered from the blood by the kidneys and released into the urine, blood levels are usually a good indicator of how well the kidneys are working. The quantity produced depends on the size 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 may be used in combination with results from other tests, such as a 24-hour urine creatinine test, to perform calculations that are used to evaluate kidney function. See the "How is it used?" section for more on these.
How is the sample collected for testing?
A blood sample is drawn from a vein in the arm. A 24-hour urine sample may also be collected, in which all urine produced during 24 hours is saved. Sometimes a single, random urine sample may be collected and tested.
NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.
Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.
Is any test preparation needed to ensure the quality of the sample?
You may be instructed to fast overnight or refrain from eating cooked meat; some studies have shown that eating cooked meat prior to testing can temporarily increase the level of creatinine. If a 24-hour urine sample is being collected, it is important to save all of the urine produced during that time period.
- 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?
Some studies have shown that eating cooked meat prior to testing can temporarily increase the level of creatinine. Creatinine levels may be 10%-30% higher in people who eat a diet that is very high in meat.
- What can I do to make my creatinine level normal?
Creatinine is a reflection of processes that are going on in your body and of kidney function. It is not generally responsive to lifestyle changes. If you have an elevated creatinine that is due to a temporary condition, such as a kidney infection, then it should normalize as the infection resolves. If it is elevated due to an underlying chronic condition that can affect kidney function, such as diabetes, then it will reflect changes in kidney function and is likely to stabilize if/when the condition is under control.
- 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 healthcare provider about all of the dietary supplements you are taking to help in the evaluation of 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 is a BUN/Creatinine ratio?
Occasionally, a health practitioner will look at the ratio between a person's BUN and blood creatinine to help determine what is causing these concentrations to be higher than normal. The ratio of BUN to creatinine is usually between 10:1 and 20:1. An increased ratio may be due to a condition that causes a decrease in the flow of blood to the kidneys, such as congestive heart failure or dehydration. It may also be seen with increased protein, from gastrointestinal bleeding, or increased protein in the diet. The ratio may be decreased with liver disease (due to decrease in the formation of urea) and malnutrition.
© 2017 American Association for Clinical Chemistry, republished from Lab Tests Online.*
Descriptions of clinical laboratory tests were originally prepared for use on Lab Tests Online, an award-winning patient education website on clinical laboratory testing. Lab Tests Online is produced by the American Association for Clinical Chemistry (AACC), a global scientific and medical professional organization dedicated to clinical laboratory science and its application to healthcare. The Lab Tests Online website is developed in collaboration with other laboratory professional societies and is funded in part through corporate sponsorships.