About the Test
Purpose of the test
The primary use of a creatinine test is to better understand how well the kidneys are working. A measurement of creatinine can be employed for screening, diagnosis, and/or monitoring of kidney problems.
Screening is trying to identify health problems before there are any signs or symptoms. If you are at higher risk of kidney problems, a creatinine test may be used to try to detect a problem early.
Diagnosis involves testing to determine the underlying cause after signs and/or symptoms have developed. Creatinine may be measured to help diagnose symptoms that can be associated with kidney problems, such as swelling in the feet, urinary changes, loss of appetite, and fatigue. A measurement of creatinine may also be included in a panel of tests for more general symptoms or when evaluating you in the emergency room.
Monitoring is how doctors track your condition over time. If you have kidney disease, a creatinine test can explain how the disease may progress. Tests of kidney function can also be used to watch for potential side effects when you have prescribed medications that can affect the kidneys.
In many cases, screening, diagnosis, and monitoring kidney problems involve more than just a creatinine measurement. For example, creatinine may be tested to calculate the estimated glomerular filtration rate (eGFR), which assesses how effectively the kidneys filter the blood.
What does the test measure?
A creatinine test measures the total amount of the substance in the blood or urine. Creatinine is a waste byproduct of the normal metabolism of creatine, a compound that provides the body’s muscles with the energy they need. In this process, some creatine breaks down into creatinine.
To clear this waste product from the body, the kidneys filter creatinine out of the blood and facilitate its removal from the body in urine.
A serum creatinine test measures the amount of creatinine in a blood sample. And a urine creatinine test measures the total amount of creatinine in all urine produced during a 24-hour period. These two values can also be compared in a creatinine clearance test.
Creatinine may be measured as part of other tests. For example, it may be included as part of a basic metabolic panel (BMP) or comprehensive metabolic panel (CMP). These tests help assess the body’s energy use, electrolyte levels, and kidney function.
When should I get this test?
A creatinine test is often prescribed when your active signs, symptoms, or overall health history reflect an elevated risk of kidney problems.
If you have symptoms that could be caused by an underlying problem affecting your kidneys, a creatinine test may be part of the diagnostic process.
But if you don’t have symptoms, your doctor may suggest a creatinine test to screen for kidney problems if you have an increased risk of kidney disease. Some risk factors for kidney disease include:
- A family history of kidney problems
- High blood pressure
If you take a medication that has the potential to affect kidney function, you may receive periodic creatinine testing to check for this side effect.
A creatinine test should first be performed to assess kidney function if you are scheduled to have a CT (computed tomography) imaging procedure with intravenous contrast.
Creatinine testing can also monitor your kidney health if you’ve had an abnormal kidney function test before or have already been diagnosed with kidney disease.
A creatinine measurement may be taken as part of a BMP or CMP during a regular health checkup. Although there is little evidence showing the benefits of this kind of screening in otherwise healthy people, some doctors prescribe these panels during routine patient care.
Finding a Creatinine Test
How can I get a creatinine test?
Creatinine tests are normally ordered by a doctor. A blood sample taken from a vein in your arm in a medical office or hospital is used for a creatinine blood test. You use special containers to collect your urine over 24 hours for a urine creatinine test.
Can I take the test at home?
Some options exist for collecting a sample for a creatinine test at home.
Urine creatinine tests are done with a 24-hour urine sample, so most doctor-prescribed urine creatinine tests require at-home collection.
Some at-home test kits include measurements of creatinine in several samples of dried urine. These samples are not analyzed at home but are sent to a lab where creatinine can be measured.
Some commercially available urine test strips change color based on the creatinine level. For urine creatinine, testing samples taken over a longer period, such as a 24-hour urine collection, are generally considered to be more accurate than testing a randomly collected spot urine sample for kidney function assessment.
At-home blood test kits include creatinine along with other measurements. These self-collection tests require mailing a blood sample to a laboratory for analysis.
How much does the test cost?
Several different factors can change the expected cost of a creatinine test, including:
- Whether the test uses a sample of blood or urine
- Whether the test measures creatinine alone or with other substances
- Where testing is done
- Whether you have health insurance coverage
The total cost may include separate charges for office visits, phlebotomy fees, or laboratory analysis. Health insurance may cover these costs if testing is prescribed by a doctor, but talk with your insurance company to find out about any out-of-pocket costs, such as a deductible or copay, for creatinine testing.
Taking a Creatinine Test
Creatinine can be measured in either blood or urine. Blood tests are normally done in a medical office or hospital and involve a routine procedure to withdraw a sample of blood from a vein in your arm.
For a urine test, you are provided containers or bags to collect all the urine you produce over a 24-hour period. Unless you are in the hospital, this requires sample collection at home that is brought to the lab.
Although less common, some at-home test kits are available to test creatinine in blood or urine without having to go to a doctor’s office or lab.
Before the test
For a blood or urine creatinine test, it’s important to follow any pretest instructions provided by your doctor.
If you are being tested for creatinine alone, you usually do not have to fast beforehand. However, you may need to avoid eating meat for around 24 hours before the test because this can affect your creatinine levels. If creatinine is being tested in a panel, you may be told to fast for eight to 12 hours before the test.
Some medications and supplements can alter creatinine levels, so your doctor may adjust your medication schedule before a creatinine test. Review all prescriptions, over-the-counter drugs, and dietary supplements you take with your doctor before having a creatinine test.
For a 24-hour urine collection, closely review the instructions with your doctor or nurse. While this collection can be inconvenient, accurately obtaining your urine samples over this full period is important to obtaining accurate results.
For at-home blood tests, look over the included instructions carefully and go through each step of the required test preparations.
During the test
If you have a blood creatinine test, a blood sample will be taken from your arm. To increase blood flow in your veins, the nurse or technician will tie elastic around the upper part of your arm. They will use an antiseptic wipe to clean the skin near a vein and insert a needle into the vein.
This type of blood test is usually over within a few minutes. While there may be a sting or some pain, it usually goes away quickly.
For a urine creatinine test, you will need to collect all the urine you produce over a 24-hour period. Most often, you are provided with special containers. On the first day of the test, you usually wake up and urinate in the toilet. After that, you collect all your urine that day and the first urination in the morning of the next day. You may also need to make notes about the times of the day when you urinate.
If you are taking an at-home blood test, you will obtain a drop of blood from your fingertip using a very small needle included in the test kit. You place that drop of blood on a strip of test paper and then package the sample to be mailed to a laboratory.
After the test
After a creatinine blood test, a bandage will be placed over the puncture site to stop it from bleeding. At that point, you can usually return to normal activities. Some pain or bruising is possible but is not typically long-lasting.
Once you have finished a 24-hour urine collection for a creatinine test, you should not have any side effects or other restrictions.
For a blood test done at home with a finger prick, you usually won’t have any lasting pain or other problems. A bandage can be used on your fingertip if it keeps bleeding after you have finished the test.
Creatinine Test Results
Receiving test results
The results from either a blood or urine creatinine test are generally available within a few business days after you take the test. You may receive a call or email from your doctor about the results, or a test report in the mail or online.
For at-home test kits that require sending your blood sample to a lab, it may take a few extra days for results to become available. With these tests, you normally access the test report through a smartphone app or website.
Interpreting test results
Creatinine tests are generally used to assess kidney function. Under normal circumstances, creatinine levels are stable, reflecting typical muscle activity and the filtering and removal of creatinine from the bloodstream.
There is no single reference range for all creatinine tests or for all people. Measurements can vary between laboratories, so it is important to look carefully at your test report to see the listed reference range for the lab that conducted your test.
Creatinine’s reference range also depends on whether it is measured in the blood or urine. The American Board of Internal Medicine lists the following reference ranges for blood and urine creatinine:
- Blood: 0.7 to 1.3 milligrams per deciliter (mg/dL) for males and 0.5 to 1.1 mg/dL for females.
- Urine: 15-25 milligrams per kilogram of body weight (mg/kg) per 24 hours.
When creatinine levels rise to abnormal levels, it may be an indication that the kidneys are not properly filtering the blood. The creatinine level may be used to calculate your eGFR, which assesses kidney filtration function.
Elevated creatinine can also be tied to dehydration, diseases that cause muscle problems, and some complications during pregnancy.
If creatinine levels are lower than expected, it may be a sign of malnutrition or conditions that provoke the loss of muscle mass.
A normal creatinine level does not guarantee kidney health. Moderate kidney impairment may not cause creatinine to rise to abnormal levels, so creatinine tests may not identify some cases of early kidney disease.
A number of individual factors, such as age, diet, and muscle mass, can affect creatinine levels, so it is important to remember your test should be interpreted with the help of your doctor in the context of your specific situation. This interpretation will also depend on why the test was ordered and whether you have any symptoms. Sometimes a doctor may prefer using a different test (such as Cystatin C) to assess a particular patient’s kidney function.
When creatinine is measured in panel tests, it may be interpreted in conjunction with other test findings. For example, the amount of creatinine relative to blood urea nitrogen (BUN), another waste product, may provide useful information for the doctor about the cause of kidney issues.
To help understand your creatinine test result, you can bring up some of the following questions when discussing the test with your doctor:
- What was the reference range for the laboratory that did my test?
- What was my creatinine level? Was it normal or abnormal?
- Are there any individual factors that might affect the accuracy or meaning of my creatinine test?
- Should I have another kidney function test now or in the future?
- Are there any other follow-up tests that you recommend? Why or why not?