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Test Findings
 
 

Hypernatraemia

 
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Overview

Hypernatraemia is a serum sodium concentration >145mmol/L. This may be caused by losing water, gaining salt or by redistribution of water within the body.

Aetiology

  • Causes of Hypernatraemia

  • Water Loss

  • Inadequate water intake
  • Diabetes insipidus (neurogenic / nephrogenic)
  • Loop diuretics
  • Acute tubular necrosis (polyuric phase)
  • Osmotic diuresis (e.g. poorly controlled diabetes)
  • Non-urinary loss - insensible, sweat, burns, diarrhoea
  • Salt Gain

  • Excessive administration - dietary excess, hypertonic saline, hypertonic dialysis
  • Endocrine - hyperaldosteronism, Cushings
  • Water Redistribution

  • Strenuous exercise
  • Seizure

Clinical Features

  • Signs and Symptoms

  • Thirst
  • Lethargy
  • Weakness
  • Confusion
  • Seizures
  • Coma

Approach

  • Interpretation

    Assess the urinary osmolality and sodium.
  • Low urine osmolality (<800mOsm/kg) - due to renal water lossDiabetes insipidus, loop diuretics, ATN, uncontrolled diabetes
  • High urine osmolality (>800mOsm/kg) - due to other causesInsensible loss, sweat, GI loss, excessive administration
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