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Sodium (Na) in Blood

Test Overview

A sodium test checks how much sodium is in the blood. Sodium is both an electrolyte and mineral. It helps keep the water (the amount of fluid inside and outside the body's cells) and electrolyte balance of the body. Sodium is also important in how nerves and muscles work.

Most of the sodium in the body (about 85%) is found in blood and lymphClick here to see an illustration. fluid. Sodium levels in the body are partly controlled by a hormone called aldosterone, which is made by the adrenal glandsClick here to see an illustration.. Aldosterone levels tell the kidneys when to hold sodium in the body instead of passing it in the urine. Small amounts of sodium are also lost through the skin when you sweat.

Most foods have sodium naturally in them or as an ingredient in cooking. Sodium is found in table salt as sodium chloride or in baking soda as sodium bicarbonate. Many medicines and other products also have sodium in them, including laxatives, aspirin, mouthwash, and toothpaste.

Low sodium levels are uncommon and are most often caused by heart failure, malnutrition, and diarrhea.

Other electrolytes, such as potassium, calcium, chloride, magnesium, and phosphate, may be checked in a blood sample at the same time as a blood test for sodium.

Why It Is Done

A blood test to check sodium levels is done to:

  • Check the water and electrolyte balance of the body.
  • Find the cause of symptoms from low or high levels of sodium.
  • Check the progress of diseases of the kidneys or adrenal glands.

How To Prepare

You do not need to do anything before having this test.


How It Is Done

Blood test

The health professional drawing blood will:

  • Clean the needle site with alcohol.
  • Put pressure to the site and then a bandage.

How It Feels






A sodium test checks how much sodium (an electrolyte and a mineral) is in the blood.


Results are ready in 1 day.


136–145 milliequivalents per liter (mEq/L) or 136–145 millimoles per liter (mmol/L)

Many conditions can affect sodium levels. Your doctor will talk with you about any abnormal results that may be related to your symptoms and past health.

High values

  • High sodium levels (hypernatremia) can be caused by a high-sodium diet or by not drinking enough water and being dehydrated. Dehydration may also be caused by medicines (such as diuretics), severe vomiting or diarrhea, Cushing's syndrome, kidney disease or injury, diabetic ketoacidosis, or a condition called diabetes insipidus that makes it hard to balance the water level in the body.
  • High sodium levels can also be caused by high levels of the hormone aldosterone (hyperaldosteronism).

Low values

What Affects the Test


What To Think About

  • When the sodium level changes quickly, you are likely to have more symptoms than when the level changes slowly. Symptoms of an abnormal sodium level include confusion, lack of energy (lethargy), or seizures.
  • To see whether the body is passing too little or too much sodium in the urine, a value called the fractional excretion of sodium (FENa) can be found by looking at the amounts of sodium and creatinine in blood and urine. In a person with kidney failure, a low FENa may mean less blood flow to the kidneys is causing the kidney failure. A urine test for sodium may be done. To learn more, see the topic Sodium (Na) in Urine.
  • Other electrolytes, such as calcium, chloride, magnesium, potassium, phosphate, blood urea nitrogen (BUN), and creatinine, may be checked in a blood sample at the same time as a blood test for sodium.




Other Works Consulted





ByHealthwise Staff
Primary Medical ReviewerAdam Husney, MD - Family Medicine
Specialist Medical ReviewerAvery L. Seifert, MD - Urology
Last RevisedSeptember 4, 2012

eMedicineHealth Medical Reference from Healthwise


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