Medical Encyclopedia: Serum sodium (Print Version)
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Medical Encyclopedia: Serum sodium
URL of this page: http://www.nlm.nih.gov/medlineplus/ency/article/003481.htm
Alternative names
Sodium - serum; Na+
Definition
This test 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 the veins below the band to swell with blood.
A needle is inserted into the vein, and the blood is collected in an airtight 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.
Because 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 one person may be more difficult than from another.
In infants or young children, the area is cleansed with antiseptic and punctured with a sharp needle or lancet. The
blood may be collected in a small glass tube (pipette), on a slide, onto a test strip, or into a small container. If
bleeding does not quickly stop, a cotton pad or bandage may be applied to the puncture site.
How to prepare for the test
Your health care provider may advise you to withhold any medications you are taking that can affect the test (see
Special Considerations.) DO NOT, however, stop or change your medications without your doctor's knowledge.
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
This test will be performed if you have symptoms of sodium imbalance or disorders associated with abnormal
sodium levels.
The level of sodium in your blood is a balance between the sodium in the food and drinks you consume and the
amount in urine. In addition, a small percent is lost through stool and sweat.
http://www.nlm.nih.gov/medlineplus/print/ency/article/003481.htm
2/22/2007
Medical Encyclopedia: Serum sodium (Print Version)
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Many factors affect sodium levels, including the hormone aldosterone, which reduces sodium loss in the urine
(aldosterone test.) ANP (atrial natriuretic protein), a hormone secreted from the heart, increases sodium loss from
the body.
Despite the tight relationship between sodium and water, the body can controls each one separately.
Normal Values
The normal range of sodium is 135 to 145 mEq/L (milliequivalents per liter).
What abnormal results mean
Higher-than-normal sodium levels may indicate 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 during a physical exam by
looking at the turgor of your skin and swelling in the ankles, feet, and legs.
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If the amount of fluid in your body (total body water) is low, you may have lost water due to excessive
sweating, diarrhea, use of diuretics (for example, furosemide, bumetanide, or torsemide), or burns.
If your total body water is normal, high sodium levels may indicate diabetes insipidus or too little of the
hormone vasopressin.
If your total body water is high, this may indicate hyperaldosteronism (too much of the hormone
aldosterone), Cushing's syndrome (too much of the hormone cortisol), or too much salt or sodium
bicarbonate ingestion.
Lower-than-normal sodium levels also may be classified according to total body water:
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Low total body water may indicate dehydration, vomiting, diarrhea, over diuresis, or ketonuria (excretion or
loss of ketone bodies in urine).
Near-normal total body water may indicate SIADH, too much of the hormone vasopressin, underactive
thyroid ( hypothyroidism), or Addison's disease (low production of cortisol and other hormones).
An increase in total body water may indicate congestive heart failure, nephrotic syndrome or other kidney
disease, or cirrhosis of the liver.
Additional conditions for which the test may be performed include:
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Acute adrenal crisis
Diabetic hyperglycemic hyperosmolar coma
Drug-induced hypothyroidism
Hepatorenal syndrome
Hypopituitarism
What the risks are
Possible risks from any blood test include:
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Excessive bleeding
Fainting or feeling lightheaded
Hematoma (blood accumulating under the skin)
Infection (a slight risk any time the skin is broken)
Multiple punctures to locate veins
Special considerations
http://www.nlm.nih.gov/medlineplus/print/ency/article/003481.htm
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Medical Encyclopedia: Serum sodium (Print Version)
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The following factors can interfere with the a test for sodium levels:
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Recent trauma, surgery, or shock
Consuming large or small amounts of salt or fluid
Intravenous fluids containing sodium
Diuretics or certain other medications
Drugs that can increase sodium levels include anabolic steroids, antibiotics, clonidine, corticosteroids, cough
medications, laxatives, methyldopa, nonsteroidal anti-inflammatory drugs (NSAIDs), and birth control pills.
Drugs that can reduce sodium levels include carbamazepine, diuretics, sulfonylureas, triamterene, and
vasopressin.
Update Date: 10/25/2006
Updated by: Robert Hurd, M.D., Department of Biology, College of Arts and Sciences, Xavier University, Cincinnati, OH. Review provided by
VeriMed Healthcare Network.
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http://www.nlm.nih.gov/medlineplus/print/ency/article/003481.htm
2/22/2007