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Hyponatraemia in clinical practice
  1. M Biswas1,
  2. J S Davies2
  1. 1Department of Medicine, Royal Gwent Hospital, Newport, Wales, UK
  2. 2Department of Medicine, University Hospital of Wales, Heath Park, Cardiff, Wales, UK
  1. Correspondence to:
 Dr J S Davies
 Department of Medicine, University Hospital of Wales, Heath Park, Cardiff CF14 4XW, Wales, UK; daviesjs{at}


Hyponatraemia is defined as a serum sodium concentration below 135 mmol/l. It causes major diagnostic and management problems in practice. Hyponatraemic disorders are divided into euvolaemic, hypervolaemic and hypovolaemic. In the evaluation of the hyponatraemic patient, history taking should focus on identifying the potential cause, duration and symptomatology. Clinical examination should include assessment of volume status. Acute hyponatraemia of less than 48 h duration requires prompt correction. Treatment may involve hypertonic saline, isotonic saline and appropriate hormone replacement therapy depending on the aetiology. Chronic hyponatraemia should be treated with caution because of the risk of central pontine myelinolysis.

  • ADH, antidiuretic hormone
  • AVP, arginine vasopressin
  • CCF, congestive cardiac failure
  • EABV, effective arterial blood volume
  • SIADH, syndrome of inappropriate ADH secretion
  • hyponatraemia
  • sodium
  • water balance
  • AVP

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  • Competing interests: None.