Serum creatinine, blood creatinine
This is a blood test that measures how well your kidneys work. Clearing and filtering waste products out of your blood are important kidney functions.
Creatinine is a normal waste product that builds up in your blood from using your muscles. Your body produces creatinine at a constant rate all the time, and healthy kidneys remove almost all of this creatinine. By comparing the amount of creatinine in your blood with a standard normal amount, your doctor can get a good idea of how well your kidneys are working.
You may have a creatinine test as part of your regular medical checkup. It's often included in routine blood tests to check your overall health.
You may need this test if you have signs or symptoms of kidney disease. Your risk for kidney disease is higher if you are an older adult, have high blood pressure, have a family history of kidney disease, or have diabetes. You may also be at increased risk if you are African-American, Hispanic, Asian, Pacific Islander, or American Indian. Signs and symptoms of kidney disease include:
Swelling in your feet or ankles
Puffiness around your eyes
Dry, itchy skin
Blood in your urine
If you are being treated for kidney disease, you may also need this test to see how well your treatment is working.
Your doctors may use your blood creatinine level, along with your age, race, sex, and other factors, to calculate your glomerular filtration rate (GFR). The GFR is considered the best measure of kidney function.
Blood urea nitrogen (BUN) is another blood test that's often done with a creatinine test. BUN is another waste product that doctors measure to see how your kidneys are functioning.
You may also have a test that measures the amount of creatinine in your urine.
Many things may affect your lab test results. These include the method each lab uses to do the test. Even if your test results are different from the normal value, you may not have a problem. To learn what the results mean for you, talk with your health care provider.
A normal level of creatinine depends on how much muscle mass you have. A normal level for a man is higher than it is for a woman. Children have lower levels than both men and women. Creatinine is measured in milligrams per deciliter (mg/dL). Here are the normal values by age:
0.9 to 1.3 mg/dL for adult males
0.6 to 1.1 mg/dL for adult females
0.5 to 1.0 mg/dL for children ages 3 to 18 years
0.3 to 0.7 mg/dL for children under age 3
If your creatinine is high, it may mean you have:
Blockage in your urinary system
Congestive heart failure
Overactive thyroid gland
If your creatinine is low, it may mean you have:
Severe liver disease
Not enough protein in your diet
The test requires a blood sample, which is drawn through a needle from a vein in your arm.
Taking a blood sample with a needle carries small risks that include bleeding, infection, bruising, and a sense of lightheadedness. When the needle pricks your arm, you may feel a slight sting or pain. Afterward, the site may be sore.
Some factors that could interfere with your creatinine test include:
Eating a lot of meat recently
Taking large doses of vitamin C
Taking certain medications, especially antibiotics
You don't need to prepare for this test. Tell your doctor if you are pregnant. Also, be sure your doctor knows about all medicines, herbs, vitamins, and supplements you are taking. This includes medicines that don't need a prescription and any illicit drugs you may use.