What Is a Sodium Blood Test?

What to expect when undergoing this test

Sodium is an electrolyte in the body. Electrolytes carry an electrical charge, and they assist the body in maintaining fluid levels inside and outside of the cells and in the blood. Sodium is crucial for your cells to be able to function properly. Your body ingests most of its sodium in the foods that you eat, and it loses sodium through sweating and urinating.

But sometimes, circumstances such as illness, diseases of the kidneys, taking medications (such as diuretics or steroids), consuming too much or too little salt, receiving IV fluids, and more can throw your sodium levels out of whack. Some of the more common symptoms of low sodium (hyponatremia) include:

  • Lethargy or fatigue
  • Confusion or disorientation
  • Muscle twitching or muscle cramps
  • Difficulty walking
  • Seizures 
  • Coma

The symptoms of too much sodium (hypernatremia) can be similar to those when the sodium levels are decreased. One main difference, however, is that elevated levels may cause a person to feel especially thirsty.

If your healthcare provider suspects there may be an imbalance in your sodium levels, they will order a sodium blood test. The sodium test may also be referred to as "Na test" (Na is the periodic symbol for sodium).

Purpose of the Test

The use of a sodium test is to determine whether your levels are too low or too high—both of which can cause a variety of symptoms ranging from moderate to severe.

It’s not uncommon for a sodium test to be done in combination with an electrolyte panel, which measures other minerals like potassium, chloride, and bicarbonate.

The test will help your doctor better understand the amount of sodium in your blood and what may be the factors causing you to feel unwell.

Risk and Contraindications

Like most blood tests, the risks and contraindications associated with a sodium test are considered slight—blood tests have a low risk of complications. However, one area where you might feel some mild discomfort is when a technician or nurse attempts to draw your blood.

A technician may discover that some people have more challenging veins from which to take a blood sample. Consequently, the technician will likely need to insert the needle more than one time, and that process can cause a bit of pain, but only temporarily.

Additional problems that could occur during a sodium blood test include:

  • a stinging sensation or minor bruising at the site of the insertion 
  • a feeling of faintness or lightheadedness
  • blood collecting under the skin (called a hematoma)
  • bleeding
  • swelling of the vein (called phlebitis)
  • infection (though the risk is low)

Note that most of the above symptoms disappear quickly, usually within a day or two. 

Also, some medications, like diuretics, antidepressants, and others, may alter your sodium levels. Let your doctor know about all the drugs you’re taking, including over-the-counter medications and supplements. Depending on your situation, your doctor might ask you to change your medication schedule for a few days before the test for the most accurate results.

Before the Test

Typically, there are no specific preparations required to have this blood test.

Timing

You should be finished with the test itself in a couple of minutes.

Location

The test may take place in your doctor's office or in another outside facility that conducts bloodwork.

What to Wear

For clothing, you can wear your usual attire. However, to allow for easy access to your veins, you may choose to wear a shirt that has sleeves you can roll up.

Food and Drink

If your healthcare provider is doing other blood tests at the same time, you might be asked to fast for several hours before the test (often, overnight).

Cost and Insurance

One the day of the test, have your insurance card and a form of identification handy so that your blood work can be billed to your insurance carrier. Before the test, you may want to talk with your insurance company about whether or not the test requires pre-approval or what your out-of-pocket expense might be.

During the Test

Many blood tests are done in a similar manner, so if you’ve had your blood taken before, this process will be more or less the same. First, you’ll likely be seated in a chair so that you can rest the arm from where the blood will be taken. The technician or nurse will place an elastic band around your arm to temporarily restrict the flow of blood and locate a vein. Once they have found the vein, they will disinfect the area using an alcohol swab or pad, then insert the needle.

After the needle has been inserted into the vein, the technician will place a small tube at the end of the syringe to collect the sample. When a sufficient amount of blood has been obtained, the technician will remove the elastic and place an adhesive or bandage over the insertion site.

After the Test

Often, blood tests of this kind are very normal, uneventful procedures. If you notice a bit of pain at the injection site, it should go away in a few days. To prevent bruising, your technician may recommend that you keep the bandage on for a few hours to decrease the likelihood of this happening.

Most of the time, there is little to no follow-up instructions after a sodium test, and you’re able to resume your regular activities.

Your healthcare provider should notify you once the results are back and provide you with any specific follow-up instructions you might need.

Interpreting the Results

If your sodium levels are elevated, it could suggest problems with the adrenal glands, kidneys, significant fluid loss, diabetes insipidus, and more.

If your sodium levels are decreased, you may be showing signs and symptoms of dehydration, overuse of medications like diuretics, Addison’s disease, heart issues, and certain kidney and liver diseases. Be sure to discuss the results of your test thoroughly with your doctor or healthcare provider. In the event you do have one of these underlying conditions, early treatment is key.

A Word From Verywell

If your test results fall outside the normal range, your doctor will help you determine the cause. Keep in mind that changes in sodium levels don’t always indicate an illness—they may fluctuate due to other factors such as the medications you’re taking. Be sure to talk to your doctor if you have questions or concerns regarding this test. 

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