Table 2.

How to diagnose SIADH?

• Determine the bare minimum: serum and urine sodium and osmolality

• Find a low serum osmolality, high urine sodium (>40 mmol/L) and osmolality (>100 mOsm/kg, often > serum osmolality)

• Find serum uric acid, urea and/or creatinine levels that are low or low normal

• Assess the extracellular fluid volume, but do not make it a decisive parameter

• Exclude diuretic use, hypothyroidism, and adrenal insufficiency (low threshold for performing the Synacthen test)

• When unsure, assess the response in serum sodium to intravenous isotonic saline