Table 1.

Diagnostic criteria for SIADH

Essential features

• Decreased effective serum osmolality (<275 mOsm/kg)

• Urinary osmolality >100 mOsm/kg during hypotonicity of the serum

• Clinical euvolaemia

• Urinary sodium >40 mmol/L with normal dietary salt intake

• Normal thyroid and adrenal function

• No recent use of diuretics

Supplemental features

• Serum uric acid <0.24 mmol/L

• Serum urea <3.6 mmol/L, low normal serum creatinine

• Fractional sodium excretion >1%, fractional urea excretion >55%

• Failure to correct hyponatraemia after 0.9% saline infusion

• Correction of hyponatraemia through fluid restriction

• Abnormal water loading test (excretion <80% of a 20 mL/kg water load in 4 h)

• Elevated vasopressin levels despite hypotonicity and clinical euvolaemiaa

Adapted from Schwartz et al. [15], Janicic and Verbalis [14] and Ellison and Berl [1].

^aDuring hyponatraemia, a measurable vasopressin level should be interpreted as too high, because under normal circumstances vasopressin should be suppressed.