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Alternative names Return to top
Sodium - serum; Na+Definition Return to top
This tests measures the amount of sodium in the blood.How the test is performed Return to top
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.
In infants or young children, 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 Return to top
The health care provider may advise you to withhold drugs that may affect the test. (See special considerations.)How the test will feel Return to top
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 Return to top
This test is performed when symptoms of a sodium imbalance are present, or when disorders associated with abnormal sodium levels develop.
Sodium (Na+) is the major positive ion in the fluids outside of cells. The concentration of sodium inside cells is only about 5 mEq/L compared with 140 mEq/L outside. The sodium content of the blood is a result of a balance between the amount in the food and beverages you consume, and the amount your kidneys excrete. (In addition, a small percent is lost through the stool and sweat.)
Many factors affect sodium levels, including the steroid hormone aldosterone, which decreases loss of sodium in the urine. (For more information, see the aldosterone test.) ANP (atrial natriuretic protein) is a hormone secreted from the heart that increases sodium loss from the body.
Despite the integral relationship between sodium and water, the body regulates them independant of each other if necessary.
Normal Values Return to top
The normal range is 135 to 145 mEq/L.What abnormal results mean Return to top
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 Return to top
Special considerations Return to top
The following factors can interfere with the test:
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Page last updated: 28 October 2004 |