Blood Sodium Level Test

Written by Christine Case-Lo
Medically Reviewed by George Krucik, MD

What Is a Sodium Blood Test?

A sodium blood test is a routine test to help your doctor learn more about your health. It is also called a serum sodium test.

Why Is the Sodium Blood Test Done?

Sodium is a mineral essential to your body. It is also referred to as Na+ or natrium. 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 drinks. 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

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

  • calcium
  • carbon dioxide (CO2)
  • chloride
  • creatinine
  • glucose
  • potassium
  • sodium
  • blood urea nitrogen (BUN)

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 (dehydration)
  • had a serious illness, recent injury, or gone through surgery
  • received intravenous (IV) 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. The sample will be 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 do not need to prepare for this test. Eat normally and drink a normal amount of water before going to the testing site.

You may have to stop taking certain medications before this test. However, drugs should only be stopped on a doctor’s instructions.

What Are the Risks of the Sodium Blood Test?

When the blood is collected, you may feel some moderate pain. There may also be 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 will 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
  • hematoma—a bruise under the skin
  • infection
  • excessive bleeding

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

Understanding the Results of a Sodium Blood Test

Normal Results

Normal results for this test are 135 to 145 mEq/L(milliequivalents per liter). However, different laboratories use different values for “normal.” Some labs go as high as 153 mEq/L.

Abnormal Results

Blood sodium levels lower than 135 mEq/L are 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 like 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 (due to too much water)
  • high levels of certain hormones, like antidiuretic hormone (ADH) or vasopressin
  • drinking too much water
  • not urinating enough
  • excessive sweating
  • ketones in the blood (ketonuria), from starvation or uncontrolled diabetes
  • underactive thyroid (hypothyroidism)
  • Addison’s disease, which decreases hormone production in the adrenal gland

Hypernatremia means high levels of sodium in the blood. It is usually defined as levels over 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 elderly 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 (diabetes insipidus)
  • high levels of aldosterone
  • glucose in urine (due to untreated diabetes mellitus)
  • 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 (NSAIDs)
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