Overview & Description
Creatinine is a waste product made by the body during regular metabolism. It is excreted into the urine by the kidneys. A serum creatinine test measures the level of creatinine in the blood.

The level of creatinine in the blood is a good measure of overall kidney function. When the kidneys are not working well for any reason, they are not able to excrete creatinine into the urine. When this happens, the level of creatinine in the blood rises.

Who is a candidate for the test?
Doctors may order this test when they think a person is dehydrated or has kidney damage. This test may also be ordered before or after a doctor prescribes certain medicines. The main reason to order the test is to make sure the kidneys are working well.

How is the test performed?
To perform a serum creatinine test, a blood sample is taken from a vein on the forearm or hand. First, the skin over the vein is cleaned with an antiseptic. Next, a strong rubber tube called a tourniquet is wrapped around the upper arm. This enlarges the veins in the lower arm by restricting blood flow through them.

A needle is gently inserted into a vein, and the tourniquet is removed. Blood flows from the vein through the needle, and is collected in a syringe or vial. After the needle is withdrawn, the puncture site is covered with a bandage for a short time to prevent bleeding. The blood sample is sent to the laboratory to determine the amount of creatinine circulating in the blood.

Results and Values
What do the test results mean?

The normal level of creatinine varies slightly based on age, body size, and sex. The level also changes during pregnancy. However, the healthy range is usually between 0.5 and 1.4 milligrams per deciliter (mg/dL).

A decreased value for this test is rarely a concern. It can occur with decreased muscle mass, such as in elderly people. Conditions such as muscular dystrophy, which is an inherited defect in muscles, can cause a low value for this test. Pregnancy may also cause a low value.

A high value for this test can occur for many reasons. Some of these reasons are described in the sections that follow.

Decreased blood flow to the kidneys
The blood flow to the kidneys can be decreased by the following conditions or events.

• severe dehydration
• massive blood loss
• congestive heart failure
• blockage in the kidney arteries, called renal artery stenosis