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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 an element necessary for your body's cells to work correctly. You can get the sodium you need through your diet. Sodium helps make sure that your nerves and muscles can work properly. Sodium is also important because it helps maintain the correct balance of fluids in your body, so that you don't have too much water. The kidneys help keep sodium at a healthy level. 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 and sodium collects in your bloodstream. This can lead to high blood pressure, which can cause other problems.

Too much sodium in the blood is a condition called hypernatremia. Too little sodium in the blood is a condition called hyponatremia. Hypernatremia can occur when you lose too many fluids, often from sweating too much, vomiting, or diarrhea. Hyponatremia can occur when you drink large amounts of water or if you have problems with the kidneys that prevent water from passing through the body normally. 

Why do I need this test?

You may need this test if your doctor suspects you have an imbalance of fluids and sodium. He or she may order this test if you have any of these symptoms, health conditions, or circumstances:

  • Diabetes that's poorly controlled Kidney problems, including advanced kidney failure

  • Loss of large amounts of bodily fluids

  • Problems with mental or cognitive function

  • Sodium therapy

  • Muscle cramps or twitching

  • Eating of large amounts of salt

  • Confusion or forgetfulness

  • Problems with walking

  • General unwell feeling

  • Nausea

  • Fatigue

  • Headaches

  • Shortness of breath

  • Fluid buildup or swelling in part of the body

  • Taking certain medicines such as diuretics, also called water pills

Your doctor also might order 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. Your doctor may order a number of tests to look at:

  • Other electrolyte levels in the blood, such as potassium

  • Concentration of the urine

  • Level of sodium in the urine

  • Concentration of the blood

  • Levels of uric acid and urea

  • Acid-base balance in the blood 

What do my test results mean?

Many things may affect your lab test results. These include the method each lab uses to do the test. Even if your test results are different from the normal value, you may not have a problem. To learn what the results mean for you, talk with your health care provider.

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 hyponatremia or low blood sodium and too much water in your body. Blood sodium levels greater than 145 mmol/L may mean you have hypernatremia, a condition in which blood sodium levels are too high for the amount of water in your body. 

How is this test done?

The test requires a blood sample, which is drawn through a needle from a vein in your arm.

Does this test pose any risks?

Taking a blood sample with a needle carries risks that include bleeding, infection, bruising, or feeling dizzy. When the needle pricks your arm, you may feel a slight stinging sensation or pain. Afterward, the site may be slightly sore. 

What might affect my test results?

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

Taking certain medications, such as diuretics and nonsteroidal anti-inflammatory drugs, can also affect your test results.

How do I get ready for this test?

Your doctor will tell you what special precautions you need to take before this test. You may need to avoid food or water for the hours before the test. Your doctor may also ask you to skip some of your medications on the day of the test. Be sure your doctor knows about all medicines, herbs, vitamins, and supplements you are taking. This includes medicines that don't need a prescription and any illicit drugs you may use.