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

There is no established system for the classification of [disease name].

OR

[Disease name] may be classified according to [classification method] into [number] subtypes/groups: [group1], [group2], [group3], and [group4].

OR

[Disease name] may be classified into [large number > 6] subtypes based on [classification method 1], [classification method 2], and [classification method 3]. [Disease name] may be classified into several subtypes based on [classification method 1], [classification method 2], and [classification method 3].

OR

Based on the duration of symptoms, [disease name] may be classified as either acute or chronic.

OR

If the staging system involves specific and characteristic findings and features: According to the [staging system + reference], there are [number] stages of [malignancy name] based on the [finding1], [finding2], and [finding3]. Each stage is assigned a [letter/number1] and a [letter/number2] that designate the [feature1] and [feature2].

OR

The staging of [malignancy name] is based on the [staging system].

OR

There is no established system for the staging of [malignancy name].

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 ↓↓	GI loss: Vomiting, diarrhea, tube drainage Insensible loss: Sweating, burns Renal loss: Salt-wasting nephropathy (Inappropriate loss of Na+-Cl– in the urine), Bicarbonaturia ( Renal tubular acidosis, Metabolic alkalosis), Osmotic diuresis Third spacing of fluids : Pancreatitis, hypoalbuminemia Cerebral salt-wasting syndrome : Stroke ,SAH (urinary salt wasting, brain natriuretic peptide ↑) Mineralocorticoid deficiency: Addison disease Excessive diuretic administration
Hypervolemic Hyponatremia	total body water ↑↑ total body sodium ↑	Renal disease: Acute or chronic kidney disease or injury (due to relatively higher water versus salt intake and poor excretion),Nephrotic syndrome Congestive heart failure Cirrhosis Iatrogenic
Euvolemic Hyponatremia	total body water ↑ total body sodium ↔	Drugs: Vasopressin, diuretics, antidepressants, opioids SIADH: Malignancy, central nervous system (CNS) disorders, pulmonary disease, or drugs, postoperative nausea, pain,stress,Neoplasia (common),trauma,pregnancy High fluid intake: Physical activity, surgery, primary polydipsia, potomania (caused by a low intake of solutes with relatively high fluid intake) Medical testing (excess fluid intake) :Colonoscopy or cardiac catheterization Hypothyroidism Glucocorticoid deficiency Reset osmostat † : Drugs, Pregnancy Iatrogenic