Cerebral salt wasting diagnosis
Criteria for cerebral salt wasting included hyponatremia <135 mEq/L, and urine output > 4 L in 12 hours with urine sodium >40 mEq/L.
Laboratory tests (serum and urinary electrolytes and osmolalities) may be identical with SIADH and CSW 1).
Furthermore, hypovolemia in CSW may stimulate ADH release. To differentiate: CVP, PCWP, and plasma volume (a nuclear medicine study) are low in hypovolemia (i.e. CSW).
The two most important differences between CSW and SIADH being extracellular volume and salt balance. An elevated serum [K+] with hyponatremia is incompatible with the diagnosis of SIADH.
1)
Nelson PB, Seif SM, Maroon JC, et al. Hyponatremia in Intracranial Disease. Perhaps Not the Syndrome of Inappropriate Secretion of Antidiuretic Hormone (SIADH). J Neurosurg. 1981; 55:938–941