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Test Findings




  • 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.


    • 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


    • 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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