Hyponatremia pathophysiology

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Pathophysiology

Term	Definitions^[1]^[2]^[3]
Hyponatremia	Hyponatremia is defined as a serum sodium concentration < 135 mEq/L.
Hypotonic hyponatremia	Hyponatremia with low osmolality (hypotonic hyponatremia) is defined as hyponatremia with a serum osmolality below 280 mOsm/kg.
Hypertonic hyponatremia	Hyponatremia with high osmolality (hypertonic hyponatremia) is defined as hyponatremia with a serum osmolality greater than 295 mOsm/kg.
Isotonic hyponatremia	Hyponatremia with normal osmolality (Isotonic hyponatremia) is defined as hyponatremia with a serum osmolality ranging between 280-295 mOsm/kg.
Hyponatremia based on ECF volume
Hypovolemic hyponatremia	Hyponatremia plus decreased extracellular cellular fluid volume. Usually diagnosed by history and physical examinationshowing water depletion plus spot urine sodium <20 to 30 mmol/L, unless kidney is the source of sodium loss.
Euvolemic hyponatremia	Hyponatremia plus normal extracellular cellular fluid volume. Majority of cases are of this type. Usually diagnosed by spot urine sodium ≥ 20 to 30 mmol/L, unless secondarily sodium depleted.
Hypervolemia hyponatremia	Hyponatremia plus increased extracellular cellular fluid volume. Usually diagnosed by history and physical examinationshowing water retention plus spot urine sodium <20 to 30 mmol/L

↑ Laczi, F. (2008). "[Etiology, diagnostics and therapy of hyponatremias]". Orv Hetil. 149 (29): 1347–54. doi:10.1556/OH.2008.28409. PMID 18617466. Unknown parameter |month= ignored (help)
↑ Douglas, I. (2006). "Hyponatremia: why it matters, how it presents, how we can manage it". Cleve Clin J Med. 73 Suppl 3: S4–12. PMID 16970147. Unknown parameter |month= ignored (help)
↑ Verbalis, JG.; Goldsmith, SR.; Greenberg, A.; Korzelius, C.; Schrier, RW.; Sterns, RH.; Thompson, CJ. (2013). "Diagnosis, evaluation, and treatment of hyponatremia: expert panel recommendations". Am J Med. 126 (10 Suppl 1): S1–42. doi:10.1016/j.amjmed.2013.07.006. PMID 24074529. Unknown parameter |month= ignored (help)