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Creatinine tests
Creatinine tests

Creatinine - serum
Definition:
Creatinine is a breakdown product of creatine, which is an important constituent of muscle. A serum creatinine test measures the amount of creatinine in the blood.

Alternative Names:
Serum creatinine

How the test is performed:
Adult or child:
Blood is drawn from a vein (venipuncture), usually from the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and a tourniquet (an elastic band) or blood pressure cuff is placed around the upper arm to apply pressure and restrict blood flow through the vein. This causes veins below the tourniquet to distend (fill with blood). A needle is inserted into the vein, and the blood is collected in an air-tight vial or a syringe. During the procedure, the tourniquet is removed to restore circulation. Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.

Infant or young child:
The area is cleansed with antiseptic and punctured with a sharp needle or a lancet. The blood may be collected in a pipette (small glass tube), on a slide, onto a test strip, or into a small container. Cotton or a bandage may be applied to the puncture site if there is any continued bleeding.
How to prepare for the test:
The health care provider may advise you to discontinue drugs that may affect the test (see special considerations).

Infants and children:
The physical and psychological preparation you can provide for this or any test or procedure depends on your child's age, interests, previous experiences, and level of trust. For specific information regarding how you can prepare your child, see the following topics as they correspond to your child's age:
How the test will feel:
When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.
Why the test is performed:
The test is performed to evaluate kidney function. If kidney function is abnormal, creatinine levels will increase in the blood, due to decreased excretion of creatinine in the urine. Creatinine levels also vary according to a persons size and muscle mass.
Normal Values:

A normal (usual) value is 0.8 to 1.4 mg/dl.

Females have a lower creatinine than males, due to decreased muscle mass.

Note: mg/dl = milligrams per deciliter
What abnormal results mean:

For abnormal results, the following applies:

Greater-than-normal levels may indicate:

Lower-than-normal levels may indicate: Additional conditions under which the test may be performed:
What the risks are:
  • Excessive bleeding
  • Fainting or feeling light-headed
  • Hematoma (blood accumulating under the skin)
  • Infection (a slight risk any time the skin is broken)
  • Multiple punctures to locate veins
Why is the test performed:
A measurement of the serum creatinine level is used to evaluate kidney function.

Creatinine is a breakdown product of creatine, which is an important constituent of muscle. Creatinine can be converted to the ATP molecule, which is a high-energy source. The daily production of creatine and subsequently creatinine, depends on muscle mass, which fluctuates very little.

Creatinine is excreted from the body entirely by the kidneys. With normal renal excretory function, the serum creatinine level should remain constant and normal.
Special considerations:
Drugs that can increase creatinine measurements include aminoglycosides (for example, gentamicin), Bactrim, cimetidine, heavy metal chemotherapeutic agents (for example, Cisplatin), and nephrotoxic drugs -- such as cephalosporins (for example, cefoxitin).
Review Date: 1/27/2002
Reviewed By: Debbie Cohen, M.D., Renal and Electrolyte Division, University of Pennsylvania Medical Center, Philadelphia, PA. Review provided by VeriMed Healthcare Network.
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