Blood test

Normal sodium level in the blood

Blood test
Normal sodium level in the blood
Last update: 16/03/2020

What is the normal level of sodium in the blood?

Adults: 135 - 145 mEq/L (135 – 145 mmol/L)
Children: 138 - 145 mEq/L (138 – 145 mmol/L)

In the International System of Units (SI), sodium in the blood is measured in mmol/L. The valence of sodium is +1 so the numeric values are the same in mmol/L or in mEq/L.

Why normal levels can differ across different labs?

Each laboratory must establish its own normal ranges for sodium in the blood. These ranges depend on the makeup of the local population, the technologies used and the accuracy of the measurement. There may be also slight differences in the normal levels according to age, gender, race or ethnic origin, geographic region, diet, type of sample and other relevant status.

Your doctor will study the results along with your medical record, screenings, physical condition, symptoms and any other relevant information about your situation.

What is the role of sodium?

Sodium is an electrolyte found mainly in the extracellular fluid. Sodium plays an important role in maintaining a correct osmolality. Osmolality measures the electrolyte-water balance of the body. Plasma osmolality measures primarily the amount of dissolved sodium in the serum (blood).

Sodium is the main electrolyte in the bodily fluids (urine, blood, stools) and its role along with potassium, chloride and CO2 (bicarbonate) is essential to maintain electrical neutrality in the cells and the acid-base balance.

Up to 90% of the human body is water. Water can be found inside the cells (two-thirds) or outside the cells (one-third). Sodium, potassium, proteins and other soluble substances are dissolved in it. The total concentration of these substances (osmolality) inside and outside the cells must be the same. That way, if there is an increase in the solutes (dissolved particles) outside the cells that pulls the water out of the cells and vice versa. Thus, sodium is a key substance to regulate osmolality.

Sodium is supplied in the food we eat. Sodium is found in salt (sodium chloride). Sodium is excreted primarily in urine by the kidneys. A little part can be excreted also through stools or sweat.

Sodium balance works as follows:

  • When the sodium level in the blood is high kidneys conserve water.
  • When the sodium level in the blood is low, kidneys get rid of excess water by urine.

Three major hormones are involved in regulating sodium and water balance in the body:

  • Aldosterone: Produced by the adrenal gland, aldosterone increases sodium and water retention in the kidneys.
  • Natriuretic hormone: Produced by the heart, natriuretic hormone promotes sodium and water excretion in the urine.
  • Antidiuretic hormone (ADH): Produced by posterior pituitary. ADH hormone promotes water retention in the kidneys.

What is a sodium blood test for?

A sodium blood test can be useful to determine your kidney function. It is usually performed along with the study of sodium in urine to get more information.

It helps also to evaluate the hormones involved in the sodium balance and estimate the hydration state of the body.

High sodium level in the blood (hypernatremia) may be due to dehydration. There are some diseases associated with hypernatremia like Cushing's syndrome or diabetes insipidus.

Abnormally low levels of sodium in the blood (hyponatremia) may be due to:

  • A low sodium diet. It is not common. Sodium levels in urine will be also low.
  • Sodium loss due to kidney diseases, Addison's disease or administration of diuretic medication. Sodium levels in urine will be high.
  • Water or fluid retention (edemas).

Where can I find more information about sodium in the blood?

You can visit our pages about:

Which values are considered a normal sodium level in the blood?

The following values are considered to be normal values:

IMPORTANT: These levels are expressed in mEq/L (mmol/L). They are an example of a healthy man of about 45 years of age with no known disease, not taking any medication and with an appropriate intake of sodium in the diet. The ranges can be different depending on the laboratory or on your personal circumstances.

135 mEq/l136 mEq/l137 mEq/l138 mEq/l139 mEq/l140 mEq/l141 mEq/l142 mEq/l
143 mEq/l144 mEq/l145 mEq/l     
Medically reviewed by Javier Muga Bustamante Ph.D. on 16/03/2020


  • Concise Book of Medical Laboratory Technology: Methods and Interpretations. 2nd Edition. 2015. Ramnik Sood. ISBN: 978-93-5152-333-8. Pag. 560.
  • Tietz. Fundamentals of Clinical Chemistry. Carl A. Burtis, Edward R. Ashwood, David E. Bruns, Barbara G. Sawyer. WB Saunders Company, 2008. Pag 432. ISBN: 978-0-7216-3865-2.
  • Common Terminology Criteria for Adverse Events (CTCAE). Version 5.0.Published: November 27, 2017. U.S. Department of health and human Services. Available on:
  • Tietz NW, ed. Clinical guide to laboratory tests, 3rd ed. Philadelphia: WB Saunders Company,1995:124pp, 502-504,562-564.
  • Matsubara A, Ichihara K, Fukutani S. Determination of reference intervals for 26 commonly measured biochemical analytes with consideration of long-term within-individual variation. Clin Chem Lab Med 2008;46:691-98.

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