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Alternative namesSodium - serum; Na+
DefinitionThis tests measures the amount of sodium in the blood.
How the test is performed
Blood is drawn from a vein, usually from the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and a band is placed around the upper arm to apply pressure and restrict blood flow through the vein. This causes veins below the band to swell 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 band 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.
How to prepare for the testThe health care provider may advise you to withhold drugs that may affect the test. (See special considerations.)
In infants and children, the preparation you can provide for this test depends on your child's age, previous experience, and level of trust. For general information regarding how you can prepare your child, see the following:
How the test will feelWhen 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
This test is performed when symptoms of a sodium imbalance are present, or when disorders associated with abnormal sodium levels develop.
Despite the integral relationship between sodium and water, the body regulates them independant of each other if necessary.
Normal ValuesThe normal range is 135 to 145 mEq/L.
Note: mEq/L = milliequivalents per liter
What abnormal results mean
Greater-than-normal sodium levels may indicate many different conditions. It is helpful to your physician to also consider the amount of fluid in your body that is outside cells (extracellular volume):
Lower-than-normal sodium levels ( hyponatremia ) may be similarly classified according to total body water:
What the risks are
Special considerationsThe following factors can interfere with the test:
Drugs that can decrease sodium measurements include carbamazepine, diuretics, sulfonylureas, triamterene, and vasopressin.
Veins and arteries vary in size from one patient to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.
Update Date: 11/17/2003David Webner, M.D., Sports Medicine Fellow, Crozer-Keystone Family Practice Program, Springfield, PA. Review provided by VeriMed Healthcare Network.
Last updated: Tue, 06 Jan 2009 00:20:03 GMT