Also Known As
Formal Name
This article was last reviewed on
This article waslast modified on May 13, 2019.
At a Glance
Why Get Tested?

To determine whether your sodium level is within normal limits; to help evaluate electrolyte balance and to help determine the cause of and monitor the treatment for illnesses associated with abnormal sodium levels in the body

When To Get Tested?

If you are experiencing dehydration, problems with blood pressure, accumulating excess fluid (edema), or have non-specific symptoms; as part of a routine health examination

Sample Required?

A blood sample drawn from a vein in your arm; sometimes a random or 24-hour urine sample

Test Preparation Needed?


You may be able to find your test results on your laboratory's website or patient portal. However, you are currently at Lab Tests Online. You may have been directed here by your lab's website in order to provide you with background information about the test(s) you had performed. You will need to return to your lab's website or portal, or contact your healthcare practitioner in order to obtain your test results.

Lab Tests Online is an award-winning patient education website offering information on laboratory tests. The content on the site, which has been reviewed by laboratory scientists and other medical professionals, provides general explanations of what results might mean for each test listed on the site, such as what a high or low value might suggest to your healthcare practitioner about your health or medical condition.

The reference ranges for your tests can be found on your laboratory report. They are typically found to the right of your results.

If you do not have your lab report, consult your healthcare provider or the laboratory that performed the test(s) to obtain the reference range.

Laboratory test results are not meaningful by themselves. Their meaning comes from comparison to reference ranges. Reference ranges are the values expected for a healthy person. They are sometimes called "normal" values. By comparing your test results with reference values, you and your healthcare provider can see if any of your test results fall outside the range of expected values. Values that are outside expected ranges can provide clues to help identify possible conditions or diseases.

While accuracy of laboratory testing has significantly evolved over the past few decades, some lab-to-lab variability can occur due to differences in testing equipment, chemical reagents, and techniques. This is a reason why so few reference ranges are provided on this site. It is important to know that you must use the range supplied by the laboratory that performed your test to evaluate whether your results are "within normal limits."

For more information, please read the article Reference Ranges and What They Mean.

Sodium Reference Range

The reference ranges1 provided here represent a theoretical guideline that should not be used to interpret your test results. Some variation is likely between these numbers and the reference range reported by the lab that ran your test. Please consult your healthcare provider.

Age Conventional Units2 SI Units3
0-18 years Not available due to wide variability. See child's lab report for reference range.
Adult 136-145 mEq/L 136-145 mmol/L
>90 years 132-146 mEq/L 132-146 mmol/L

1 from Tietz Textbook of Clinical Chemistry and Molecular Diagnostics. Burtis CA, Ashwood ER, Bruns DE, eds. 5th edition, St. Louis: Elsevier Saunders; 2011.

2 Conventional Units are typically used for reporting results in U.S. labs

3 SI Units are used to report lab results outside of the U.S.

What is being tested?

Sodium is an electrolyte present in all body fluids and is vital to normal body function, including nerve and muscle function. This test measures the level of sodium in the blood and/or urine.

Sodium, along with other electrolytes such as potassium, chloride, and bicarbonate (or total CO2), helps cells function normally and helps regulate the amount of fluid in the body. While sodium is present in all body fluids, it is found in the highest concentration in the blood and in the fluid outside of the body's cells. This extracellular sodium, as well as all body water, is regulated by the kidneys.

We get sodium in our diet, from table salt (sodium chloride or NaCl), and to some degree from most of the foods that we eat. Most people have an adequate intake of sodium. The body uses what it requires and the kidneys eliminate the rest in the urine. The body tries to keep the blood sodium within a very narrow concentration range. It does this by:

  • Producing hormones that can increase (natriuretic peptides) or decrease (aldosterone) the amount of sodium eliminated in urine
  • Producing a hormone that prevents water losses (antidiuretic hormone, ADH, sometimes called vasopressin)
  • Controlling thirst; even a 1% increase in blood sodium will make a person thirsty and cause that person to drink water, returning the sodium level to normal.

Abnormal blood sodium is usually due to some problem with one of these systems. When the level of sodium in the blood changes, the water content in the body also changes. These changes can be associated with too little fluid (dehydration) or with too much fluid (edema), often resulting in swelling in the legs.

How is the sample collected for testing?

A blood sample is taken by needle from a vein in the arm. In some cases, a random or 24-hour urine sample may be required.

Is any test preparation needed to ensure the quality of the sample?

No test preparation is needed.

Accordion Title
Common Questions
  • How is it used?

    A sodium blood test is used to detect abnormal concentrations of sodium, including low sodium (hyponatremia) and high sodium (hypernatremia). It is often used as part of an electrolyte panel or basic metabolic panel for a routine health checkup.

    Sodium is an electrolyte present in all body fluids and is vital to normal body function, including nerve and muscle function. It helps cells function normally and helps regulate the amount of fluid in the body.

    A blood sodium test may also be used to detect the cause and help monitor treatment in people with dehydration, excess fluid (edema), or with a variety of symptoms (e.g., weakness, confusion, thirst and/or dry mucous membranes). Blood sodium can be abnormal in many diseases. A health practitioner may order this test, along with other electrolytes, to identify an electrolyte imbalance or if there are symptoms of illness involving the brain, lungs, liver, heart, kidney, thyroid, or adrenal glands.

    In people with a known electrolyte imbalance, a blood sodium test may be used to monitor the effectiveness of treatment or to monitor people taking medications that can affect sodium levels, such as diuretics.

    Urine sodium levels may be tested in people who have abnormal blood sodium levels to help determine whether an imbalance is due to, for example, consuming too much sodium or losing too much sodium. Urine sodium testing is also used for people with abnormal kidney tests to help the healthcare practitioner determine the cause of kidney disease and to help guide treatment.

  • When is it ordered?

    Sodium testing is a part of the routine lab evaluation of most people as part of an electrolyte panel or a basic metabolic panel. These may be ordered during an annual physical or when someone has non-specific health complaints.

    A blood sodium test may be ordered when a person has symptoms of low sodium, such as weakness, confusion, and lethargy. If the sodium level falls quickly, the person may feel weak and fatigued; in severe cases, the person may experience confusion or even fall into a coma. When the sodium level falls slowly, however, there may be no symptoms. That is why sodium levels are often checked even if someone has no symptoms.

    Sodium blood testing may be ordered when a person has symptoms of high sodium, such as thirst, dry mucous membranes (e.g., mouth, eyes), less frequent urination, muscle twitching, and/or agitation. If the sodium level rises to extremely high concentrations, symptoms can include restlessness, acting irrationally, and coma or convulsions.

    Electrolytes may be measured when monitoring treatment involving intravenous (IV) fluids or when there is a possibility of developing dehydration. Electrolyte panels and basic metabolic panels are also commonly ordered on a regular basis when monitoring treatment of certain conditions, including high blood pressure, heart failure, and liver and kidney disease.

    A urine sodium test may be ordered when a blood sodium test result is abnormal to help determine the cause of the imbalance or to monitor treatment.

  • What does the test result mean?

    A low level of blood sodium (hyponatremia) may be due to:

    • Losing too much sodium, most commonly from conditions such as diarrhea, vomiting, excessive sweating, use of diuretics, kidney disease or low levels of cortisol, aldosterone and sex hormones (Addison disease)
    • Drinking too much water as might occur during exercise
    • Excess fluid accumulation in the body (edema) caused by heart failure, cirrhosis, and kidney diseases that cause protein loss (nephrotic syndrome) or malnutrition. In a number of diseases, particularly those involving the brain and the lungs, many kinds of cancer, and with some drugs, the body makes too much anti-diuretic hormone (ADH), causing a person to keep too much water in the body.

    Low blood sodium is rarely due to decreased sodium intake (deficient dietary intake or deficient sodium in IV fluids).

    A high blood sodium level (hypernatremia) is almost always caused by losing too much water (dehydration) without drinking enough water. In rare cases, it may be due to increased salt intake without enough water, Cushing syndrome, or a condition caused by too little ADH called diabetes insipidus.

    Sodium urine concentrations must be evaluated in association with blood levels. The body normally elimiates excess sodium, so the concentration in the urine may be elevated because it is elevated in the blood. It may also be elevated in the urine when the body is losing too much sodium; in this case, the blood level would be normal to low. If blood sodium levels are low due to insufficient intake, then urine concentrations will also be low.

    • Decreased urinary sodium levels may indicate dehydration, congestive heart failure, liver disease, or nephrotic syndrome.
    • Increased urinary sodium levels may indicate diuretic use or Addison disease.

    Sodium levels are often evaluated in relation to other electrolytes and can be used to calculate a quantity termed anion gap. The anion gap is useful in identifying the presence of unknown substances such as toxins in the blood.

  • Is there anything else I should know?

    Certain drugs such as anabolic steroids, antibiotics, corticosteroids, laxatives, cough medicines, and oral contraceptives may cause increased levels of sodium. Other drugs such as ACE inhibitors, diuretics, carbamazepine, heparin, and tricyclic antidepressants may cause decreased levels of sodium.

  • What is the recommended dietary salt intake?

    The Food and Nutrition Board recommends a sodium intake of less than 2300 mg per day for adults. People normally obtain adequate amounts of sodium in their daily diet, but it is important not to exceed this recommended maximum amount.

    Common dietary sources of sodium are often processed food to which salt is added during preparation, such as cheeses, soups, pickles, and pretzels. Additionally, other processed, commercially prepared, or restaurant foods are generally high in sodium.

    For people who are sodium-sensitive or have hypertension, reducing sodium intake can lead to markedly beneficial health effects. But even if you don't have high blood pressure, limiting sodium as part of a healthy diet may decrease your risk of developing blood pressure problems and heart disease.

    Your taste for salt is both acquired and reversible. As you use less salt, your preference for it will lessen.

  • Is anyone at particular risk for low or high sodium levels?

    Yes. People who have prolonged diarrhea and/or vomiting, profuse sweating, burns, Addison disease, kidney disease, or congestive heart failure may have low sodium levels. People with dehydration, diuretic use, Cushing syndrome, cystic fibrosis, neurological disorders, hypothyroidism, or renal failure may have high sodium levels.

  • Should athletes and others pay particular attention to re-hydrating after playing sports or exercising to keep their sodium levels up?

    Yes. During prolonged and strenuous exercise, both water and sodium are lost through sweating. To maintain the correct balance of water and sodium in the body, people may need not only to drink water but to ensure adequate sodium intake, whether through salty foods or specially formulated "sports drinks."

View Sources

Sources Used in Current Review

Harrison, P. (2015 August 14). Low-Normal Serum Sodium Identified as a Risk Factor for CVD/Death. Medscape Multispecialty. [On-line information]. Available online at Accessed 8/15/15.

Craig, S. (2015 August 5, Updated). Hyponatremia in Emergency Medicine. Medscape Drugs & Diseases [On-line information]. Available online at Accessed 8/15/15.

Lukitsch, I. (2015 March 21, Updated). Hypernatremia. Medscape Drugs & Diseases [On-line information]. Available online at Accessed 8/15/15.

Dugdale, D. (2013 October 29, Updated). Sodium blood test. MedlinePlus Medical Encyclopedia [On-line information]. Available online at Accessed 8/15/15.

Dugdale, D. (2013 April 14, Updated). Hyponatremia. MedlinePlus Medical Encyclopedia [On-line information]. Available online at Accessed 8/15/15.

Mir, F. (2013 December 5, Updated). Serum Sodium. Medscape Drugs & Diseases. [On-line information]. Available online at Accessed 8/15/15.

Sources Used in Previous Reviews

Tietz. Fundamentals of Clinical Chemistry, 2001; Fifth edition. Elsevier Health Sciences.

Boh, LE. Pharmacy Practice Manual, 2001; Second edition. Lippincott Williams & Wilkins.

NewsTarget. Pass on the Salt: News Release. Friday, August 18, 2006. Available online through Accessed January 2008.

Jacobs & DeMott. Laboratory Test Handbook, 2001; 5th edition. Lexi-Comp, Inc.

Tietz Textbook of Clinical Chemistry and Molecular Diagnostics. Burtis CA, Ashwood ER, Bruns DE, eds. St. Louis: Elsevier Saunders; 2006.

Clarke, W. and Dufour, D. R., Editors (2006). Contemporary Practice in Clinical Chemistry, AACC Press, Washington, DC.

Food and Nutrition Board. Institute of Medicine of the National Academies, Dietary Reference Intake Tables, Water and Electrolytes. PDF available for download at

Wu, A. (2006). Tietz Clinical Guide to Laboratory Tests, Fourth Edition. Saunders Elsevier, St. Louis, Missouri.

Pagana K, Pagana T. Mosby's Manual of Diagnostic and Laboratory Tests. 3rd Edition, St. Louis: Mosby Elsevier; 2006.

Thomas, Clayton L., Editor (1997). Taber's Cyclopedic Medical Dictionary. F.A. Davis Company, Philadelphia, PA [18th Edition].

Pagana, Kathleen D. & Pagana, Timothy J. (2001). Mosby's Diagnostic and Laboratory Test Reference 5th Edition: Mosby, Inc., Saint Louis, MO.

(1995-2004). Minerals and Electrolytes. The Merck Manual of Medical Information Second Home Edition [On-line information]. Available online through

Ben-Joseph, E., Reviewed (2004 July). Dehydration. Information for Parents [On-line information]. Available online through

A.D.A.M. editorial, Updated (2003 October 15). Electrolytes. MedlinePlus Medical Encyclopedia [On-line information]. Available online at

Pagana K, Pagana T. Mosby's Manual of Diagnostic and Laboratory Tests. 4th edition, Pp. 479-482; 989-992.

USDA. Dietary Guidelines for Americans, 2010. Available online at Accessed August 2011. Hyponatremia. Available online at Accessed August 2011.

Ask a Laboratory Scientist

This form enables patients to ask specific questions about lab tests. Your questions will be answered by a laboratory scientist as part of a voluntary service provided by one of our partners, American Society for Clinical Laboratory Science. Please allow 2-3 business days for an email response from one of the volunteers on the Consumer Information Response Team.

Thank you for using the Consumer Information Response Service ("the Service") to inquire about the meaning of your lab test results.  The Service is provided free of charge by the American Society for Clinical Laboratory Science, which is one of many laboratory organizations that supports Lab Tests Online.
Please note that information provided through this free Service is not intended to be medical advice and should not be relied on as such. Although the laboratory provides the largest single source of objective, scientific data on patient status, it is only one part of a complex biological picture of health or disease. As professional clinical laboratory scientists, our goal is to assist you in understanding the purpose of laboratory tests and the general meaning of your laboratory results. It is important that you communicate with your physician so that together you can integrate the pertinent information, such as age, ethnicity, health history, signs and symptoms, laboratory and other procedures (radiology, endoscopy, etc.), to determine your health status. The information provided through this Service is not intended to substitute for such consultations with your physician nor specific medical advice to your health condition.
By submitting your question to this Service, you agree to waive, release, and hold harmless the American Society for Clinical Laboratory Science and its affiliates or their past or present officers, directors, employees, agents, and Service volunteers (collectively referred to as "ASCLS") and the American Association  for Clinical Chemistry and its affiliates or their past or present officers, directors, employees, agents, and Service volunteers (collectively referred to as "AACC") from any legal claims, rights, or causes of action you may have in connection with the responses provided to the questions that you submit to the Service.
AACC, ASCLS and its Service volunteers disclaim any liability arising out of your use of this Service or for any adverse outcome from your use of the information provided by this Service for any reason, including but not limited to any misunderstanding or misinterpretation of the information provided through this Service.