Hyponatremia differential diagnosis

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Iqra Qamar M.D.[2] Saeedeh Kowsarnia M.D.[3]

Overview

Hyponatremia must be differentiated from other diseases that cause muscle weakness or cramps, oliguria, vomiting or diarrhea and seizures.

Differentiating Hyponatremia from other Diseases

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Hyponatremia serum sodium < 135 mEq/L

check for pseudohyponatremia (Hyperglycemia, Hyperlipidemia, Hyperproteinemia, lab errors)

Symptomatic

Asymptomatic

confusion, ataxia, seizures, obtundation, coma, respiratory depression

Determine serum osmolality Serum Osmolality = (2 x (Na + K)) + (BUN (mg/dL) / 2.8) + (glucose (mg/dL) / 18) + (Ethanol (mg/dL) /3.7)

Infuse 3% saline (1 to 2 mL per kg per hour) with goal of increasing serum sodium level by 6 to 8 mEq per L (not to exceed 10 to 12 mEq per L in the first 24 hours or 18 mEq per L in 48 hours) Consider desmopressin, 1 to 2 mcg every four to six hours

Give single intravenous bolus of 100 to 150 mL 3% saline with goal of increasing serum sodium level by 2 to 3 mEq per L; check sodium level every 20 minutes until symptoms resolve; may repeat bolus twice if symptoms do not resolve

Normal 275-295 mOsm/kg Isotonic hyponatremia (pseudohyponatremia)

Low <275mOsm/kg Hypotonic hyponatremia

High >295 mOsm/kg Hypertonic hyponatremia

Assess for hyperproteinuria or hyperlipidemia

Assess volume status

Assess for hyperglycemia, check for mannitol or sorbitol use or recent administration of radiocontrast media

Symptom resolution

Evaluate vital signs, orthostatics, jugular venous pressure, skin turgor, mucous membranes, peripheral edema, and blood urea nitrogen and uric acid levels

Check serum sodium level every two hours; adjust infusion rate and switch to isotonic saline

Determine underlying cause

Hypovolemic (decreased total body water and sodium level)

Euvolemic (increased total body water, normal total body sodium level)

Hypervolemic (increased total body water)

Urinary sodium > 20 mEq per L

Urinary sodium < 20 mEq per L

Urinary sodium usually > 20 mEq per L

Urinary sodium < 20 mEq per L

Urinary sodium > 20 mEq per L

Renal loss (from diuretics or mineralocorticoid deficiency)

Extrarenal loss (fromv omiting, diarrhea,third spacing, or bowel obstruction)

Urinary osmolality > 100 mOsm per kg

Urinary osmolality < 100 mOsm per kg

Variable urinaryosmolality

Heart failure,cirrhosis, nephrosis,hypoalbuminemia

Renal failure

Isotonic saline(see Table 1for specifitreatments)

Isotonic saline(see Table 1for specifictreatments)

Syndrome ofinappropriate antidiuretichormonesecretion, hypothyroidism,adrenal insufficiency,stress, drug use

Primary polydipsia,low solute intake (beer potomania syndrome)

Resetosmostat

Diuresis, fluid andsodium restriction(see Table 1 for specific treatments)

Fluid and sodium restriction, dialysis (see Table 1 for specific treatments)

Fluid restriction(see Table 1for specifictreatments)

Fluid restriction(see Table 1for specific treatments)

Fluid restriction(see Table 1for specifictreatments)

Disease	Clinical manifestations												Paraclinical Findings
	Symptoms and Signs												Lab Findings
	Muscle weakness/ Cramps	Seizures	Oliguria	Vomiting/ Diarrhea	Volume status	JVP	Edema	Crackles	Ascites	Tachycardia	Hypotension	Dry mucous membranes	Urine Analysis			Serum Osmolality	ADH levels
													Urine Na	Urine Osm	FeNa
Renal failure	+/-	+/-	+/-	-	Hypervolemic	+	+	+	+	-	-	-	>20	-	>1%	-	Normal or ↑
Congestive heart failure	+/-	+/-	-	-	Hypervolemic	+	+	+	+	-	-	-	<10	-	<1%	-	↑
Cirrhosis	+/-	+/-	-	-	Hypervolemic	+	+	+	+	-	-	-	<10	-	<1%	-	↑
SIADH	+/-	+/-	-	-	Euvolemic	-	-	-	-	-	-	-	-	>100	-	-	↑
Hypothyroidism	+/-	+/-	-	-	Euvolemic	-	-	-	-	-	-	-	-	>100	-	-	↑
Adrenal insufficiency	+/-	+/-	-	-	Euvolemic	-	-	-	-	-	-	-	-	>100	-	-	↑
Psychogenic polydipsia	+/-	+/-	-	-	Euvolemic	-	-	-	-	-	-	-	-	<100	-	-	↑
Beer drinker's potomania	+/-	+/-	-	-	Euvolemic	-	-	-	-	-	-	-	-	<100	-	-	↓
Pregnancy	+/-	+/-	-	-	Euvolemic	-	-	-	-	-	-	-	-	Variable	-	-	↓
Anorexia (Chronic malnutrition)	+/-	+/-	-	-	Euvolemic	-	-	-	-	-	-	-	-	Variable	-	-	-
Diuretic induced hyponatremia	+/-	+/-	+	-	Hypovolemic	-	-	-	-	+	+	+	>20	-	>1%	-	-
Non oliguric ATN	+/-	+/-	-	-	Hypovolemic	-	-	-	-	+	+	+	>20	-	>1%	-	-
Diseases causing 3rd spacing (Pancreatitis, SBO)	+/-	+/-	+	+/-	Hypovolemic	-	-	-	-	+	+	+	<10	-	<1%	-	-
Gastroenteritis	+/-	+/-	+	+	Hypovolemic	-	-	-	-	+	+	+	<10	-	<1%	-	-
Sweating	+/-	+/-	+	-	Hypovolemic	-	-	-	-	-	+/-	+/-	<10	-	<1%	-	-
Cerebral salt-losing syndrome