sodium test checks how much sodium (an
electrolyte and a mineral) is in the blood. Sodium is
both an electrolyte and mineral. It helps keep the water (the amount of fluid
inside and outside the body's cells) and electrolyte balance of the body.
Sodium is also important in how nerves and muscles work.
the sodium in the body (about 85%) is found in blood and
lymph fluid. Sodium levels in the body are partly
controlled by a
hormone called aldosterone, which is made by the
adrenal glands. Aldosterone levels tell the kidneys
when to hold sodium in the body instead of passing it in the urine. (See a
picture of the
adrenal glands or the
kidneys .) Small amounts of sodium are also lost
through the skin when you sweat.
Most foods have sodium naturally
in them or as an ingredient in cooking. Sodium is found in table salt as sodium
chloride or in baking soda as sodium bicarbonate. Many medicines and other
products also have sodium in them, including laxatives, aspirin, mouthwash, and
Too much sodium in the diet may raise blood pressure
in some people. For those who have high blood pressure, eating foods with a lot
of sodium makes their chance of heart disease,
stroke, and kidney damage higher.
Heart failure gets worse when too much sodium is
eaten. It increases the amount of water the body holds in and this causes
swelling of the legs and hands. Some people have problems when they eat more
than 4,000 milligrams (mg) of sodium per day.
Low sodium levels
are uncommon and most often occur as a side effect of taking medicines that
make you urinate more, such as
diuretics. Severe diarrhea or vomiting or heavy
sweating may also cause low sodium levels.
such as potassium, calcium, chloride, magnesium, and phosphate, may be checked
in a blood sample at the same time as a blood test for sodium.
Why It Is Done
A blood test to check sodium levels is
- Check the water and electrolyte balance of the
- Find the cause of symptoms from low or high levels of
- Check the progress of diseases of the kidneys or adrenal
How To Prepare
You do not need to do anything before
having this test.
Talk to your doctor about any
concerns you have regarding the need for the test, its risks, how it will be
done, or what the results will mean. To help you understand the importance of
this test, fill out the
medical test information form(What is a PDF document?).
How It Is Done
The health professional drawing blood
- Wrap an elastic band around your upper arm to
stop the flow of blood. This makes the veins below the band larger so it is
easier to put a needle into the vein.
- Clean the needle site with
- Put the needle into the vein. More than one needle stick
may be needed.
- Attach a tube to the needle to fill it with
- Remove the band from your arm when enough blood is
- Put a gauze pad or cotton ball over the needle site as
the needle is removed.
- Put pressure to the site and then a