Hyponatremia classification

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Saeedeh Kowsarnia M.D.[2]

Overview

hyponatremia, serum sodium less than 135 mEq/L (mmol/L),is classified based on ADH level, duration of hyponatremia, serum osmolality and volume status.

Classification

Hyponatremia is defined as serum sodium less than 135 mEq/L (mmol/L) .There are different classifications for hyponatremia based on duration, severity, volume status, ADH level and serum osmolality.

Hyponatremia is classified based on serum sodium level to :

• Mild : Serum sodium 130– 135 mmol/L
• Moderate:  Serum sodium ≤125–129 mmol/L
• Severe: Serum sodium <124 mmol/L

Classification based on duration :

• Hyper acute : Develops in a few hours, excess water intake, impaired water excretion, runners, users of the recreational drug (Ecstasy)

• Acute: Rapid onset <48 hours, surgeries, colonoscopy preparation, polydipsia, diuretics
• Chronic: Gradual onset >48 hours, caused by chronic disease ( including cardiac, renal, hepatic and other conditions)

( Etiologies cause hyperacute and acute hyponatremia are applicable to each category interchangeably depending on the onset of symptoms)

Classification based on ADH level :

• ↑ ADH: Volume depletion (GI loss, Renal loss) , decreased perfusion ( CHF, Cirrhosis), increased ADH secretion, reset osmostat

• ↓ ADH: Primary polydipsia, ↓ dietary solute intake, advanced renal failure

Classification based upon osmolality :

• Hypertonic hyponatremia: Serum osmolality >295 mOsm/kg
• Hypotonic hyponatremia: Serum osmolality < 275 mOsm/kg
• Norotonic hyponatremia: Serum osmolality 275–295 mOsm/kg

According to volume status :

Volume status	Sodium status	Causes
Hypovolemic Hyponatremia	total body water ↓ total body sodium ↓↓	True volume depletion:GI loss,Renal loss,Insensible loss
Euvolemic Hyponatremia	total body water ↑ total body sodium ↔	Drugs, Increased ADH level,Reset osmostat,Low dietary salt intake
Hypervolemic Hyponatremia	total body water ↑↑ total body sodium ↑	Decrease effective arterial volume: Cirrhosis, Renal disease, CHF