Hyponatremia laboratory findings

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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

An elevated/reduced concentration of serum/blood/urinary/CSF/other [lab test] is diagnostic of [disease name].

OR

Laboratory findings consistent with the diagnosis of [disease name] include [abnormal test 1], [abnormal test 2], and [abnormal test 3].

OR

[Test] is usually normal among patients with [disease name].

OR

Some patients with [disease name] may have elevated/reduced concentration of [test], which is usually suggestive of [progression/complication].

OR

There are no diagnostic laboratory findings associated with [disease name].

Laboratory Findings

Biochemical evaluation for finding the etiologies of hyponatremia :

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2

For approach to differential diagnosis click here.

For the clinical approach to diagnosis click here.

Conditions	Sodium status	Plasma osmolality	Urine osmolality	Differentiation of causes
Hypervolemic hyponatremia	TBW ↑↑ Serum Na ↑	< 275 mOsm/kg	> 100 mOsm/kg	UNa > 20 mEq/L urinary sodium: Acute or chronic renal failure Fluid overload Psychogenic polydipsia Diuretic use in: Heart failure , Liver disease, Nephrotic syndrome UNa < 20 mEq/L urinary sodium: Heart failure Cirrhosis Nephritic/nephrotic syndrome
Euvolemic hyponatremia	TBW ↑ Serum Na ↔	< 275 mOsm/kg	> 100 mOsm/kg	Variable UNa: SIADH/SIAD UNa > 40 mEq/L: Cortisol deficiency Hypothyroidism Drugs SIADH/SIAD
Hypovolemic hyponatremia	TBW ↔ Serum Na ↓↓	≥ 280 mOsm/kg	> 500 mOsm/kg	UNa > 30 mEq/L: Renal loss: Osmotic diuresis (glucose, urea, bicarbonaturia) Salt-Iosing nephropathy Addison disease CSW UNa < 30 mEq/L:

Characteristics	Hypervolemic Hyponatremia	Euvolemic Hyponatremia	Hypovolemic Hyponatremia
Total body water	↑↑	↑	↔
Serum sodium level	↑	↔	↓↓
Plasma Osmolality, mOsm/kg	< 280	<280	≥ 280
Urine Osmolality, mOsm/L	> 100	> 100	> 500
Urine sodium level, mEq/L	< 20 or >20	> 20	< 10 or > 20
Differentiation of causes	> 20 mEq/L urinary sodium: Acute or chronic renal failure Fluid overload Psychogenic polydipsia < 20 mEq/L urinary sodium: Heart failure Cirrhosis Nephritic syndrome	SIADH/SIAD Adrenal insufficiency Hypothyroidism Drugs	< 10 mEq/L urinary sodium: Diuretics Extrarenal loss such as diarrhea, vomiting Severe hyperglycemia Third spacing of fluids > 20 mEq/L urinary sodium: Adrenal insufficiency Renal bicarbonate loss(renal tubal acidosis, metabolic alkalosis) Renal sodium loss (cerebral salt wasting, salt-wasting nephropathy) Diuretics

• There are no diagnostic laboratory findings associated with [disease name].

OR

• An elevated/reduced concentration of serum/blood/urinary/CSF/other [lab test] is diagnostic of [disease name].
• [Test] is usually normal among patients with [disease name].
• Laboratory findings consistent with the diagnosis of [disease name] include:
  • [Abnormal test 1]
  • [Abnormal test 2]
  • [Abnormal test 3]

• Some patients with [disease name] may have elevated/reduced concentration of [test], which is usually suggestive of [progression/complication].