How It Feels

The blood sample is taken from a vein in your arm. An elastic band is wrapped around your upper arm. It may feel tight. You may feel nothing at all from the needle, or you may feel a quick sting or pinch.

Risks

There is very little chance of a problem from having blood sample taken from a vein.

• You may get a small bruise at the site. You can lower the chance of bruising by keeping pressure on the site for several minutes.
• In rare cases, the vein may become swollen after the blood sample is taken. This problem is called phlebitis. A warm compress can be used several times a day to treat this.
• Ongoing bleeding can be a problem for people with bleeding disorders. Aspirin, warfarin (Coumadin), and other blood-thinning medicines can make bleeding more likely. If you have bleeding or clotting problems, or if you take blood-thinning medicine, tell your doctor before your blood sample is taken.

Results

A sodium test checks how much sodium (an electrolyte and a mineral) is in the blood.

The normal values listed here-called a reference range-are just a guide. These ranges vary from lab to lab, and your lab may have a different range for what’s normal. Your lab report should contain the range your lab uses. Also, your doctor will evaluate your results based on your health and other factors. This means that a value that falls outside the normal values listed here may still be normal for you or your lab.

Results are ready in 1 day.

Many conditions can affect sodium levels. Your doctor will talk with you about any abnormal results that may be related to your symptoms and past health.

High values

• High sodium levels (hypernatremia) can be caused by a high-sodium diet or by not drinking enough water and being dehydrated. Dehydration may also be caused by severe vomiting or diarrhea, Cushing's syndrome, kidney disease or injury, diabetic ketoacidosis, or a condition called diabetes insipidus that makes it hard to balance the water level in the body.
• High sodium levels can also be caused by high levels of the hormone aldosterone (hyperaldosteronism).

Low values

• Low sodium levels (hyponatremia) can be caused by a lot of sweating, burns, severe vomiting or diarrhea, drinking too much water (psychogenic polydipsia), or poor nutrition.
• Low sodium levels can also be caused by underactive adrenal glands or thyroid gland, heart failure, kidney disease, cirrhosis, cystic fibrosis, or SIADH (syndrome of inappropriate antidiuretic hormone secretion).

What Affects the Test

Reasons you may not be able to have the test or why the results may not be helpful include:

• Taking medicines, such as birth control pills, corticosteroids, antibiotics, estrogens, tricyclic antidepressants, heparin, nonsteroidal anti-inflammatory drugs (NSAIDs), diuretics, lithium, and many medicines used to treat high blood pressure.
• Having high levels of glucose, triglycerides, or protein.
• Getting sodium in intravenous (IV) fluids given during a recent surgery or hospitalization.