Serum Sodium

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Latest Edit: Iva Lloyd, ND 2021-08-24 (EDT)

See Also Lab Tests

Sodium constitutes 90% of the electrolyte fluid and is the most prevalent cation in the extra-cellular fluid. It is a major part of the sodium-potassium pump, facilitating cellular transport. It also acts as the main base of the blood and functions in maintaining osmotic pressure, acid-base balance, aiding in nerve impulse transmission, as well as renal, cardiac, and adrenal functions.[1],[2]


Serum sodium changes tend to be affected more by changes in fluid balance, body water and functional issue such as adrenal dysfunction, than by changes in sodium/salt balance. Urinary sodium is considered to be a more sensitive indicator of altered sodium/salt balance than blood.

Mechanisms for maintaining a constant and steady level of plasma and extracellular sodium include:

  • Renal blood flow
  • Carbonic anhydrase enzymatic activity
  • Aldosterone
  • Renin enzymatic secretion
  • Antidiueretic hormone (ADH)/Vasopressin

Patient Preparation

  • Food or fluid is not restricted.
  • Factors which can cause increased levels
  • recent trauma, surgery, or shock
  • Drugs: anabolic steroids, antibiotics, clonidine, corticosteroids, cough medicines, laxatives, methyldopa, carbenicillin, estrogens, oral contraceptives, NSAIDS, aspirin, anti-hypertensives, laxatives
  • Factors which can cause decreased levels
  • high triglycerides, low protein levels
  • Drugs: carbamazepine, diuretics, sodium-free IV fluids, sulfonylureas, triamterene, angiotensin-converting enzyme inhibitors, captopril, haloperidol, heparin, nonsteroidal antiinflammatory drugs, tricyclic antidepressants, vasopressin, laxatives, sulfates.

Clinical Implications

Ranges: The following are the reference ranges for this lab. However, lab ranges can vary by laboratory and country. [2]

Standard U.S. Units Standard International Units
Conventional Laboratory Range 135-145 mEq/L 135-145 mmol/L
Optimal Range 135-142 mEq/L 135-142 mmol/L
Alarm Ranges <125 or >155 mEq/L <125 or >155 mmol/L

High levels indicate:

Low levels indicate:

Associated Tests


  1. Pagana Kathleen D, Pagana Timothy J (1998) Mosby's Manual of Diagnostic and Laboratory Tests, Mosby, Inc
  2. 2.0 2.1 Weatherby Dicken, Ferguson Scott (2002) Blood Chemistry and CBC Analysis: Clinical Laboratory Testing from a Functional Perspective, Bear Mountain