What is the role of lab studies in the workup of cerebral salt- cerebral salt-wasting syndrome (CSWS) (renal salt wasting)?

Updated: May 13, 2020
  • Author: Sudha Garimella, MBBS; Chief Editor: Sasigarn A Bowden, MD  more...
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Failure to distinguish cerebral salt-wasting syndrome (renal salt wasting) from SIADH as the cause of hyponatremia may lead to improper therapy (ie, fluid restriction), thereby exacerbating intravascular volume depletion and potentially jeopardizing cerebral perfusion.

The following lab studies may be indicated in patients with cerebral salt-wasting syndrome:

  • Serum sodium concentration - Patients with untreated cerebral salt-wasting syndrome are often hyponatremic

  • Serum osmolality - If measured serum osmolality exceeds twice the serum sodium concentration and azotemia is not present, suspect hyperglycemia or mannitol as the cause of hyponatremia

  • Urinary output - Urine flow rate is often high in cerebral salt-wasting syndrome; urine flow rate is low in SIADH

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