Definition of Creatinine

Creatinine is filtered from the body via the kidneys.
Creatinine is filtered from the body via the kidneys.. MediaForMedical/UIG/Getty Images

What is Creatinine?

Creatinine is a by-product that is produced when muscles expend energy. In the muscles, creatine is used to generate energy for muscle action and creatinine is one of the resulting molecules. Creatinine is normally filtered from the blood by the kidneys and excreted in the urine.

Blood Test for Creatinine

The body generates a constant amount of creatinine. The muscles turnover about 2% of their creatine into creatinine each day.

The body relies on good kidney function to filter it out into the urine. With properly functioning kidneys, the blood levels of creatinine should be in a constant range. The normal range for serum creatinine is 0.7 to 1.3 mg/dL for men and 0.6 to 1.1 mg/dL for women., with normal ranges varying from lab to lab.

Creatinine levels in the blood can be used to check on kidney metabolism and are part of usual screening tests for renal function. The serum creatinine level is commonly checked along with the blood urea nitrogen level (BUN), and the ratio between them is compared. Both are waste products of protein metabolism and are elevated when the kidneys are not functioning well. The ratio between them is elevated in dehydration, gastrointestinal bleeds and kidney failure. But it is very non-specific and only a clue in a diagnosis.

Other blood tests that are typically run as part of a renal function panel are electrolytes (sodium, potassium, chloride, bicarbonate), glucose, phosphorus, albumin, and calcium.

The results of all of these can point to how well the kidneys are functioning.

Should I Worry If My Doctor Orders a Creatinine Test?

Creatinine is also one of the tests commonly included in a Chem 7 panel, along with the electrolytes, glucose and BUN. A basic metabolic panel or Chem 8 is similar, with the addition of calcium.

These panels are often run as health screening tests as part of a check-up and to monitor patients who are under any medical care. It should be no special cause for concern to see these panels ordered. A renal function panel may also be ordered simply to provide a more comprehensive screening for any problems that are not obvious.

Creatinine Levels in Diabetes

One of the complications of type 2 diabetes is kidney damage that can result in kidney failure. When kidneys start to fail, creatinine builds up in the blood. Doctors will watch the creatinine levels carefully to determine how much function the kidneys have. A normal level of creatinine is usually As the number rises above 1.2 mg/dl, it shows that kidney function is decreasing. Creatinine levels are obtained by a simple blood test.

Creatinine Clearance Test

This test is also performed to check kidney function and how well blood is flowing through the kidneys and how well the glomeruli in the kidneys are working to filter the blood. It a 24-hour urine collection sample and a blood sample is also drawn at the end of the collection period.

You have to take a jug (or two) home with you and collect all of your urine for 24 hours and return it to the laboratory for testing.

The volume of the urine is used in calculating the creatinine clearance, so the total amount of urine you produce in 24 hours is an important part of the test. The concentration of creatinine in the urine is measured as well as the concentration in the blood. All together they are used to derive the creatinine clearance rate.

A decreased creatinine clearance rate means less creatinine is being eliminated through the kidneys. If the blood creatinine is also high, this indicates a problem with kidney function and/or the blood flow to the kidneys.

Normal values may vary from lab to lab, but these are a general range:

  • Male: 97 to 137 ml/min.
  • Female: 88 to 128 ml/min.


Creatinine blood test, MedlinePlus, U.S. National Library of Medicine. Updated 8/4/2013.

Creatinine clearance test. MedlinePlus. U.S. National Library of Medicine. Updated 8/25/2013.

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