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

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%	↓	↑
SIAD/ 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	+/-	+/-	-	+/-	Euvolemic	-	-	-	-	-	+/-	-	>20	>100	> 1%	↓	-

Approach to differential diagnosis

Serum Na ≤ 135 meq/L

Check for: • Serum osmolality • Urine osmolality • Urea • Glucose • Urine chloride • Urine Na

Normotonicity 275–295 mOsm/kg •Hyperlipidemia •Hyperproteinemia •Glycine

Hypertonicity > 295 mOsm/kg • Glucose • Mannitol • Glycine

Hypotonicity <275 mOsm/kg

UOsm < 100mOsm/kg

UOsm > 200mOsm/kg

UOsm 100–200mOsm/kg

Conditions •Polydipsia •↓ solute excertion (Beer potomania ,Tea & toast diet)

Conditions •Polydipsia •↓ solute excertion (Beer potomania ,Tea & toast diet) •Rule out SIAD

Hypovolemia Based on history & physical exam

Hypervolemia

Euvolemia

UNa < 30 mEq/L

Variable UNa

UNa > 30 mEq/L

UNa < 30 mEq/L

UNa > 30 mEq/L

Variable UNa

UNa < 20 mEq/L

> 20 UNa < 40 mEq/L

UNa > 40 mEq/L

Extrarenal losses •Vomiting (Ucl ↓) •Diarrhea •Pancreatitis •Sweating •Small bowel obstruction

Variable UNa •Diuretic use Discontinue diuretics if UNa is still abnormal

Renal losses •Osmotic diuresis (glucose, urea,bicarbonaturia) •Salt-Iosing nephropathy •Addison disease •CSW

Conditions •Heart failure •Liver disease •Nephrotic syndrome

Conditions •Chronic kidney disease •Diuretic use in: Heart failure Liver disease Nephrotic syndrome

Discontinue diuretics if PNa normalize it's not SIAD if it's not normalized

Probable hypovolemia

Hypovolemia or euvolemia

•Probable euvolemia •SIAD •Cortisol deficiency •Hypothyroidism

Administer 0.9% saline

Normalize PNa

Administer 1–2 L 0.9% saline

Failure to normalize PNa

Hypovolemia

PNa decreases or no change

PNa increases

Decreasing UOsm

No change in UOsm but UNa increases

SIAD

No change in UOsm but UNa increases

Decreased UNa

Hypovolemia

Salt-depleted SIAD

Hypovolemia

Decreasing Uosm

Administer additional saline

No change in UOsm but UNa increases

Salt-depleted SIAD