Patient education: Sodium test (The Basics)

What is a sodium test? — Sodium is one of many substances in the body called "electrolytes" that help carry signals between cells. A sodium test measures the concentration of sodium in blood. This means how much water is in the blood compared with sodium:

●A high concentration of sodium means that there is too little water compared with sodium. The medical term for this is "hypernatremia." Some problems that can cause hypernatremia include:

•Diabetes insipidus

•Dehydration

•Salt poisoning

●A low concentration of sodium means that there is too much water compared with sodium. The medical term for this is "hyponatremia." Some problems that can cause hyponatremia include:

•Heart failure

•Cirrhosis (a severe form of liver disease)

•Kidney disease

•Lung disease

Sodium is usually measured as part of other blood tests, such as an "electrolyte panel" or "basic metabolic panel." These tests measure the amount of sodium, plus other substances, in blood.

Why might I need a sodium test? — Your doctor might order a sodium test to:

●Check if you have an electrolyte or fluid imbalance

●See how treatment is working if you have been diagnosed with hypernatremia or hyponatremia

How do I prepare for a sodium test? — For this test, you need to get a "blood draw." Your doctor or nurse will tell you where to go for this. You don't need to "fast" (avoid eating or drinking) before this test. But if you are having other tests on the same day, your doctor or nurse might tell you to fast before those tests.

It might help to wear a short-sleeve shirt to your blood draw appointment. This makes it easier for the person drawing your blood to get to your arm.

What happens during a blood draw? — For the blood draw, a needle is used to take a small amount of blood from your arm (figure 1). Collecting the blood only takes a few minutes. The blood is then tested in a lab.

Tell the person who takes your blood:

●If you take "blood thinner" medicines or if you have a bleeding problem – They will make sure that your bleeding is under control before you leave.

●If you have a latex allergy – Some of the supplies used for blood draws might contain latex.

●If you have a preferred arm to use

Most of the time, getting blood taken does not cause problems. You might have a little soreness or bruising where the needle went in.

What do my results mean? — Your doctor or nurse will tell you when to expect your results, and will contact you with the results. Or if you use an online "patient portal," you might get an alert there when your results are ready.

If your sodium test shows any abnormal results, your doctor or nurse will talk to you about what to do next. They might need to do more tests to figure out what the cause is.

If you do have a health problem, your doctor will work with you to come up with a plan for treatment.

More on this topic

Patient education: Electrolyte panel (The Basics)
Patient education: Basic metabolic panel (The Basics)
Patient education: Hyponatremia (The Basics)