Table 4.

Biochemical and water changes in the syndrome of inappropriate ADH secretion (SIADH), cerebral salt wasting syndrome (CSWS) and diabetes insipidus (DI)

Finding	SIADH	CSWS	DI
Plasma volume	Raised	Lowered	Lowered
Sodium balance	Positive/equal	Negative	Equal
Water balance	Positive	Negative	Negative
Serum sodium	Low	Low	High
Serum osmolality	Lowered	High/normal	High
Urine sodium	High	High	Normal
Urine osmolality	High	Normal/high	Low

(Normal values: Plasma osmolality 278–305 mmol/kg, Plasma sodium 135–145 mmol/L, urine osmolality 350–1000 mmol/kg, urine sodium 20–60 mmol/L : 100–250 mmol/24hr)