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Blood Sodium Test

What is a sodium blood test?

A sodium blood test is a routine test that allows your doctor to see how much sodium is in your blood. It’s also called a serum sodium test. Sodium is an essential mineral to your body. It’s also referred to as Na+.

Sodium is particularly important for nerve and muscle function. Your body keeps sodium in balance through a variety of mechanisms. Sodium gets into your blood through food and drink. It leaves the blood through urine, stool, and sweat. Having the right amount of sodium is important for your health. Too much sodium can raise your blood pressure.

A lack of sodium can cause symptoms such as:

  • nausea
  • vomiting
  • exhaustion
  • dizziness

When do you receive a sodium blood test?

The sodium blood test is often part of a basic metabolic panel. This is a group of related tests. The basic metabolic panel includes tests for:

  • calcium
  • bicarbonate
  • chloride
  • creatinine
  • glucose
  • potassium
  • sodium
  • blood urea nitrogen

Blood sodium can also be part of an electrolyte panel. Electrolytes are substances that carry an electrical charge. Potassium and chloride are other electrolytes.

This test may be ordered if you have:

  • eaten large amounts of salt
  • not eaten enough or had enough water
  • a serious illness, or gone through surgery
  • received intravenous fluids

You may also receive this test to monitor medications that affect your sodium levels. These include diuretics and certain hormones.

How is the sodium blood test done?

This test is performed on a blood sample, obtained by venipuncture. A technician will insert a small needle into a vein on your arm or hand. This will be used to fill a test tube with blood.

How do I prepare for the sodium blood test?

You don’t need to prepare for this test. Consume a normal amount of food and water before going to the testing site. You may have to stop taking certain medications before this test. But, drugs should only be stopped on a doctor’s instruction.

What are the risks of the sodium blood test?

When the blood is collected, you may feel some moderate pain or a mild pinching sensation. Any discomfort should only last a short time. After the needle is taken out, you may feel a throbbing sensation. You’ll be instructed to apply pressure to the puncture. A bandage will be applied.

There are few risks to taking a blood sample. Rare problems include:

  • lightheadedness or fainting
  • a bruise near the area the needle was inserted, also known as hematoma
  • infection
  • excessive bleeding

If you bleed for a long period after your test, it may indicate a more serious condition. Excessive bleeding should be reported to your doctor.

Understanding the results of a sodium blood test

Your doctor will go over your results with you. Results range from normal to abnormal.

Normal results

Normal results for this test are 135 to 145 mEq/L (milliequivalents per liter), according to the Mayo Clinic. But different laboratories use different values for "normal."

Abnormally low levels

A blood sodium level lower than 135 mEq/L is called hyponatremia. Symptoms of hyponatremia include:

  • fatigue
  • nausea and vomiting
  • headache
  • loss of appetite
  • confusion or disorientation
  • hallucinations
  • loss of consciousness or coma

Hyponatremia can cause damage to cells. It makes them swell up with too much water. This may be particularly dangerous in areas such as the brain.

Hyponatremia is more often a problem in older adults. It can be caused by:

  • diuretics
  • antidepressants
  • certain pain medications
  • large burns on the skin
  • kidney disease
  • liver disease or cirrhosis
  • severe diarrhea or vomiting
  • heart failure
  • high levels of certain hormones, such as antidiuretic hormone or vasopressin
  • drinking too much water
  • not urinating enough
  • excessive sweating
  • ketones in the blood, known as ketonuria
  • underactive thyroid, or hypothyroidism
  • Addison’s disease, which is low hormone production in the adrenal gland

Abnormally high levels

Hypernatremia means high levels of sodium in the blood. It’s defined as levels that exceed 145 mEq/L. Symptoms of hypernatremia include:

  • thirst
  • fatigue
  • swelling in hands and feet
  • weakness
  • insomnia
  • rapid heartbeat
  • coma

Hypernatremia is most often a problem in older adults, infants, and people who are bedridden. Causes of hypernatremia include:

  • not drinking enough water
  • drinking salty water
  • eating too much salt
  • excessive sweating
  • diarrhea
  • low levels of hormones such as vasopressin
  • high levels of aldosterone
  • Cushing’s syndrome, caused by excessive cortisol

Certain medications can also potentially cause hypernatremia. These include:

  • birth control pills
  • corticosteroids
  • laxatives
  • lithium
  • nonsteroidal anti-inflammatory pain medications

The takeaway

A blood sodium test is ordered by your doctor for a number of reasons. Sometimes it’s needed because you may be on certain medications that affect the sodium levels in your blood. Other times it may be part of a general health checkup. Either way it’s important to know how much sodium in your blood. Keeping it at the optimum level is good for your overall health.

Content licensed from:

Written by: Christine Case-Lo
Medically reviewed on: Sep 13, 2016: University of Illinois-Chicago, College of Medicine

This feature is for informational purposes only and should not be used to replace the care and information received from your health care provider. Please consult a health care professional with any health concerns you may have.
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