Sodium
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- Also Known As:
- Na

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At a Glance
Why Get Tested?
To determine whether your sodium level is within normal limits; as part of an electrolyte panel or metabolic panel to help diagnose and determine the cause of an electrolyte imbalance; to help monitor treatment for illnesses that can cause abnormal sodium levels in the body
When To Get Tested?
When you have a routine health exam; when you are experiencing dehydration, problems with blood pressure, accumulating excess fluid (edema), or have non-specific symptoms
Sample Required?
A blood sample drawn from a vein; sometimes a random or 24-hour urine sample is collected.
Test Preparation Needed?
None
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.
Electrolytes are minerals that carry a charge and exist in your body fluids. Sodium and other electrolytes such as potassium, chloride, and bicarbonate (or total CO2) help 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 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.
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.
Common Questions
View Sources
Sources Used in Current Review
2019 review performed by Adrienne N. Eckhardt, BS, MT(ASCP) and the LTO Editorial Review Board.
(November, 20, 2017) Martin, L. Electrolytes. MedlinePlus Medical Encyclopedia. Available online at https://medlineplus.gov/ency/article/002350.htm. Accessed on June 26, 2019.
Greenstein, M. 24-Hour Urine Collection. University of Rochester Medical Center Health Encyclopedia. Available online at https://www.urmc.rochester.edu/encyclopedia/content.aspx?ContentTypeID=92&ContentID=P08955. Accessed on June 26, 2019.
(January 9, 2018) Stephens, C. Urine Sodium Level Test. Healthline. Available online at https://www.healthline.com/health/sodium-urine. Accessed on June 26, 2019.
Sources Used in Previous Reviews
Tietz. Fundamentals of Clinical Chemistry, 2001; Fifth edition. Elsevier Health Sciences.
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NewsTarget. Pass on the Salt: News Release. Friday, August 18, 2006. Available online through http://www.mayoclinic.org. Accessed January 2008.
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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 http://www.iom.edu.
Wu, A. (2006). Tietz Clinical Guide to Laboratory Tests, Fourth Edition. Saunders Elsevier, St. Louis, Missouri.
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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 http://www.medscape.com/viewarticle/849532. Accessed 8/15/15.
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Dugdale, D. (2013 April 14, Updated). Hyponatremia. MedlinePlus Medical Encyclopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/000394.htm. Accessed 8/15/15.
Mir, F. (2013 December 5, Updated). Serum Sodium. Medscape Drugs & Diseases. [On-line information]. Available online at http://emedicine.medscape.com/article/2099065-overview. Accessed 8/15/15.
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