Routinely as part of a comprehensive metabolic panel (CMP) or basic metabolic panel (BMP) when you have a health exam; 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
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 the urine produced during that time period.
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 amount of creatinine you produce depends on your body size and your muscle mass. For this reason, creatinine levels are usually slightly higher in men than in women and children.
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 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 still can be used by the body. The remaining waste forms urine.
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 calculate values that are used to evaluate kidney function.
How is the test used?
The creatinine blood test is used to assess kidney function. It is frequently ordered along with a BUN (blood urea nitrogen) test as part of a basic or comprehensive metabolic panel (BMP or CMP), groups of tests that are done to evaluate the health of your major organs. A BMP or CMP may be used to screen people during routine physical exams or to help evaluate people who seek medical care in the emergency room and/or are admitted to the hospital. Sometimes, creatinine may be performed as part of a renal panel to evaluate kidney function.
If the creatinine and BUN tests are found to be abnormal or if you have 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 your kidney function 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 if not cleared rapidly.
Results from creatinine tests may be used to estimate the amount of blood filtered per minute by the kidneys. This is known as the estimated glomerular filtration rate (eGFR). GFR is difficult to measure directly. Estimated GFR is used to screen for and detect early kidney damage, to help diagnose chronic kidney disease (CKD), and to monitor kidney status.
- Blood creatinine measurements, along with age, race, and sex, are used to calculate the eGFR. The National Kidney Disease Education Program, American Society of Nephrology, and the National Kidney Foundation all recommend that an eGFR be calculated every time a creatinine blood test is done.
- Another, less common way to obtain GFR is to calculate creatinine clearance. There are several versions of the creatinine clearance calculation. All of them include the measurement of the amount of creatinine in a blood sample collected just before or after the urine collection, the amount of creatinine in a 24-hour urine sample, and the 24-hour urine volume.
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. Examples include:
- Urine albumin to creatinine ratio (ACR). This calculation 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 to creatinine ratio (UP/CR). This calculation 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 during a routine health exam. It may also be ordered when your healthcare practitioner suspects that your kidneys are not working properly due to your signs and symptoms. 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
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?
BUN and creatinine levels that are within the ranges established by the laboratory performing the test suggest that your kidneys are functioning as they should.
Increased creatinine and BUN levels in the blood may mean that your kidneys are not working as they should. Your healthcare practitioner will consider other factors, such as your medical history and physical exam, to determine what, if any, condition may be affecting your kidneys.
Some examples of conditions that can increase creatinine levels 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
- Conditions that can block the flow of urine in the urinary tract, such as prostate disease or kidney stone
- 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 and are 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. These results are usually used as references for other substances measured in the urine and to calculate ratios. For example urine albumin results are compared to urine creatinine and a urine albumin/creatinine ratio (ACR) is calculated to provide a more accurate indication of the how much albumin is being released into the urine. Elevated urine albumin may indicate kidney damage, but since the amount of albumin in the urine can vary considerably, an elevated ACR should be repeated twice within 3 to 6 months to confirm the diagnosis.
My creatinine result is slightly out of range. What does this mean?
Your creatinine result is interpreted by your healthcare provider within the context of other tests that you have had done as well as other factors, such as your medical history. A single result that is slightly high or low may or may not have medical significance. This is why a healthcare practitioner may repeat a test on you and why they may look at results from prior times when you had the same test performed.
However, a result outside the range may indicate a problem and warrant further investigation. Your healthcare provider will evaluate your test results in the context of other relevant factors to determine whether a result that falls outside of the reference range means something significant for you.
For more, read the article Reference Ranges and What They Mean.
Will exercise affect my creatinine levels?
How does diet affect creatinine levels?
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 return to normal 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 or 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?
What is a BUN/Creatinine ratio?
Occasionally, a healthcare 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.
Why would a urine creatinine be ordered along with a urine drug test?
When people are having drugs-of-abuse testing performed, they may try to "trick the system" by diluting their urine with water (directly or by drinking lots of water) or by adding another adulterating substance to the urine. Since creatinine is produced and released into the urine at a constant rate, it should be present in a normal concentration. The test can be ordered, along with other tests such as a pH and specific gravity and/or tests for adulterants, to help evaluate the validity of a urine sample. If the creatinine is lower than typically seen in a human urine, then it is more likely that the sample has been tampered with or that the person has had too much water to drink. In both of these cases, the urine sample will not be considered suitable for testing and will need to be recollected.
Is there anything else I should know?
Creatinine blood levels can 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.