Creatinine

Creatinine is a 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 or urine with a standard normal amount, your health care provider can get a good idea of how well your kidneys are working. Your provider can test your creatinine levels two ways: by testing a blood sample or urine sample.

Why do I need this test?

You may need this test if your health care provider suspects you have a problem with your kidneys. Signs and symptoms of kidney disease include:

  • Frequent tiredness
  • Swelling in your feet or ankles
  • Poor appetite
  • Puffiness around your eyes
  • Dry, itchy skin
  • Muscle cramps
  • Frequent urination
  • Foamy urine
  • Painful urination
  • Blood or protein in your urine
  • Difficulty sleeping

You may also have this test if you have already been diagnosed with chronic kidney disease, so that your health care provider can check your kidney function regularly and adjust your treatment if needed.

What other tests might I have along with this test?

Your healthcare provider may also order a protein-to-creatinine ratio test done on your urine. This will look at the amount of protein compared with creatinine. Excess protein that has leaked into your urine may be a sign of kidney disease.

Your healthcare provider may also order blood tests to measure your kidney function. These might include a creatinine blood test and a blood urea nitrogen, or BUN, test. The creatinine blood test is used to find out your creatinine clearance, which gives a good measure of kidney function.

What do my test results mean?

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:

  • Kidney disease
  • Blockage in your urinary system
  • Muscle disease
  • Congestive heart failure
  • Diabetes
  • Dehydration
  • Overactive thyroid gland
  • Shock

If your creatinine is low, it may mean you have:

  • Muscle loss
  • Severe liver disease
  • Not enough protein in your diet