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This test measures the concentration of sodium in the blood.
Blood is drawn from a vein, usually from the inside of the elbow or the back of the hand. The site is cleaned with germ-killing medicine (antiseptic). The health care provider wraps an elastic band around the upper arm to apply pressure to the area and make the vein swell with blood.
Next, the health care provider gently inserts a needle into the vein. The blood collects into an airtight vial or tube attached to the needle. The elastic band is removed from your arm.
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, a sharp tool called a lancet may be used to puncture the skin and make it bleed. The blood collects into a small glass tube called a pipette, or onto a slide or test strip. A bandage may be placed over the area if there is any bleeding.
Your health care provider will instruct you, if necessary, to discontinue drugs that may interfere with the test. Do not stop or change your medications without your doctor's knowledge.
Drugs that can increase blood sodium levels include:
Drugs that can reduce blood sodium levels include:
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.
Your doctor may order this test if you have signs of a sodium imbalance or disorders associated with abnormal sodium levels.
Your blood sodium level represents a balance between the sodium and water in the food and drinks you consume and the amount in urine. A small percentage is lost through stool and sweat.
Many factors affect sodium levels, including:
The normal range for blood sodium levels is 135 to 145 milliequivalents per liter (mEq/L).
Normal value ranges may vary slightly among different laboratories. Talk to your doctor about the meaning of your specific test results.
The examples above show the common measurements for results for these tests. Some laboratories use different measurements or may test different specimens.
Abnormal sodium levels can be due to many different conditions. To help determine the cause, your health care provider will consider the total amount of fluid in your body. This is done by looking at the turgor of your skin and swelling in the ankles, feet, and legs.
For greater than normal sodium levels (hypernatremia):
For lower than normal sodium levels (hyponatremia):
Additional conditions for which the test may be performed include:
Possible risks from any blood test include:
Shorecki K, Ausiello D. Disorders of sodium and water homeostasis. In: Goldman L, Ausiello D, eds. Cecil Medicine. 23rd ed. Philadelphia, PA: Saunders Elsevier; 2007:chap 117.
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