Sodium (Blood)

Does this test have other names?

Na test

What is this test?

This test measures the levels of sodium in your blood. Sodium is a substance your body's cells need to work normally. Sodium helps make sure that your nerves and muscles can work as they should. Sodium is also important because it helps maintain the right balance of fluids in your body. The kidneys help keep sodium at a healthy level. You can get the sodium you need through your diet. But it's easy to take in too much sodium through your diet. When your body has too much sodium, your kidneys can't remove enough of it. Sodium collects in your bloodstream. This can lead to high blood pressure, which can cause other problems.

Too much sodium in the blood is called hypernatremia. Too little sodium in the blood called hyponatremia. Hypernatremia can occur when you lose too many fluids. This can happen from sweating too much, vomiting, or diarrhea. Hyponatremia can occur when you drink large amounts of water or if you have problems with your kidneys that affect your ability to urinate. 

Why do I need this test?

You may need this test if your healthcare provider thinks you have an imbalance of fluids and sodium. You may have symptoms such as:

  • Problems with mental or cognitive function
  • Muscle cramps or twitching
  • Cravings for large amounts of salt
  • Confusion or forgetfulness
  • Problems with walking
  • General unwell feeling
  • Nausea
  • Tiredness (fatigue)
  • Headaches
  • Shortness of breath
  • Fluid buildup or swelling in part of the body

The test can check for:

  • Diabetes that's not controlled well
  • Kidney problems, including advanced kidney failure

Or you may need this test if you:

  • Are taking certain medicines such as water pills (diuretics)
  • Are having sodium therapy
  • Lost a large amounts of bodily fluids
  • You may also have this test as part of a routine health check. 

What other tests might I have along with this test?

You may need other tests along with a sodium blood test. You may have tests to look at:

  • Other electrolyte levels in your blood, such as potassium
  •  Concentration of your urine
  • Level of sodium in your urine
  • Concentration of your blood
  • Levels of uric acid and urea
  • Acid-base balance in your blood 

What do my test results mean?

Test results may vary depending on your age, gender, health history, the method used for the test, and other things. Your test results may not mean you have a problem. Ask your healthcare provider what your test results mean for you. 

Normal sodium levels are usually between 136 and 145 millimoles per liter (mmol/L). Blood sodium levels below 136 mmol/L may mean you have low blood sodium (hyponatremia). Blood sodium levels greater than 145 mmol/L may mean you have blood sodium levels that are too high (hypernatremia). 

How is this test done?

The test is done with a blood sample. A needle is used to draw blood from a vein in your arm or hand. 

Does this test pose any risks?

Having a blood test with a needle carries some risks. These include bleeding, infection, bruising, and feeling lightheaded. When the needle pricks your arm or hand, you may feel a slight sting or pain. Afterward, the site may be sore. 

If your blood sample is collected incorrectly, your test results may be affected. Having high blood sugar (hyperglycemia) can also affect your test results.

Taking some medicines can also affect your test results. These include diuretics and nonsteroidal anti-inflammatory medicines such as ibuprofen.

How do I get ready for this test?

Your healthcare provider will tell you what you need to do before this test. You may need to not have food or water for several hours before the test. You may need to not take some of your medicines on the day of the test. Be sure your healthcare provider knows about all medicines, herbs, vitamins, and supplements you are taking. This includes medicines that don't need a prescription and any illegal drugs you may use. 

© 2000-2018 The StayWell Company, LLC. 800 Township Line Road, Yardley, PA 19067. All rights reserved. This information is not intended as a substitute for professional medical care. Always follow your healthcare professional's instructions.

Instructions for Hypernatremia

You have been diagnosed with hypernatremia. This means you have too much sodium (salt)  in the blood. It can be caused by a high salt intake. But it's more often due to fluid loss. Loss of too much fluid can occur if the kidneys excrete too much urine. This is called polyuria. Fluid loss can also be caused by excessive sweating. This can happen during hot weather or exercise. It can be caused by diarrhea or vomiting. It can also be caused if you don't drink enough water. If not treated right away, it is a seriouis problem that can cause a seizure or a loss of consciousness. It can also lead to death. 

Symptoms of hypernatremia include:

  • Extreme thirst
  • Fatigue
  • Confusion
  • Low blood pressure

Diet changes

Limit all foods that are high in sodium, including: 

  • Canned soups
  • Canned beans
  • Frozen dinners
  • Commercially prepared tomato sauce and spaghetti sauce
  • Pizza
  • Potato and corn chips
  • Salted pretzels and crackers
  • Olives
  • Pickles
  • Sauerkraut
  • Soy sauce
  • Cottage, american, or feta cheeses
  • Canned chili and stew
  • Lunch meats
  • Processed meats, such as hot dogs and salami
  • Instant hot cereal
  • Quick breads made with baking soda or baking powder, including pancakes, bisquits, waffles, and muffles
  • Packaged dessert mixes

Other home care

  • Drink more fluids as advised.
  • Have your sodium levels checked as often as advised by your healthcare provider. This is very important if you are taking a diuretic. This is a medicine that helps flush water from the body.
  • Replace your body fluids after vomiting or diarrhea. Ask your healthcare provider for the best way to do this.
  • Tell your doctor about all medicines you are taking. These include both prescribed and over-the-counter medicines. Some of these can raise sodium levels.
  • Take all medicine as directed.

Follow-up care

Follow up with your healthcare provider, or as advised.  Your healthcare provider will need to watch your condition closely. You may need extra care if you have a health condition that causes your hypernatremia.

When to call your healthcare provider

Call  your healthcare provider right away if you have any of the following:

  • Muscle twitching, spasms or cramps
  • Farigue
  • Confusion
  • Seizures
  • Loss of consciousness or fainting
  • Dizziness or lightheadedness


Hyponatremia means low sodium levels in the blood. This condition most often occurs after prolonged vomiting or diarrhea, which causes your body to lose too much water and sodium. It can also result from drinking excess amounts of water or the use of diuretics (water pills). Rarely, it can be associated with disorders of your endocrine system, as side effects of illicit drug use (ecstasy), as a complication of some cancers especially small cell lung cancer, or as a complication of renal and liver disease or heart failure.

Mild hyponatremia causes no symptoms. It is only discovered with a blood test. As sodium levels in the blood decreases, symptoms begin to appear. This includes weakness, confusion, muscle cramping and seizures.

Home care

  • Reduce your daily water intake until the problem is corrected.
  • If you have been taking diuretics, you may be asked to stop taking them for a short time.
  • If you are having symptoms of weakness or confusion, do not drive or operate dangerous machinery until symptoms resolve.
  • If your sodium levels are too low to be managed at home with the above recommendations, you will be asked to go to the hospital to have your sodium replaced through your vein.

Follow-up care

Follow up with your healthcare provider for a repeat blood test within the next week, or as advised.

When to seek medical advice

Call your healthcare provider if any of the following occur:

  • Increasing weakness
  • Dizziness
  • Irregular heartbeat, extra beats or very fast heart rate
  • Increasing confusion
  • Fainting or loss of consciousness
  • Seizure

Instructions for Hyponatremia

You were diagnosed with hyponatremia, which means your blood level of sodium (salt) is too low. Salt is needed for the body and brain to work. Very low blood levels of sodium can be fatal. Symptoms can include headache, confusion, fatigue, muscle cramps, hallucinations, seizures, and coma. You have been treated to raise your blood levels of sodium. These instructions will help you care for yourself at home as you have been instructed.

Home care

  • Limit your intake of fluids. Drink only the amounts directed by your healthcare provider.
  • Ask your healthcare provider what you should use to replace fluids if you are throwing up.
  • Keep all follow-up appointments. Your provider needs to watch your condition closely.

To help prevent hyponatremia:

  • Take all medicines exactly as directed. Certain medicines can lower blood sodium levels.
  • If you have done something that makes you sweat a lot, drink fluids that contain salt and other electrolytes. 
  • Tell all healthcare providers what medicines you take. Mention all prescription and over-the-counter drugs and herbs.
  • Have your sodium levels checked often. This is vital if you take a diuretic (medicine that helps your body get rid of water).


Follow up with your healthcare provider, or as advised. 

When to call your healthcare provider

Call your provider right away if you have any of the following:

  • Severe tiredness
  • Fainting
  • Dizziness
  • Loss of appetite
  • Nausea or Vomiting
  • Confusion or forgetfulness
  • Muscle spasms, cramping or twitching
  • Seizures
  • Gait disturbances

Disclaimer: The UCLA Health System cannot guarantee the accuracy of such information. The information is provided without warranty or guarantee of any kind. Please speak to your Physician before making any changes.