The cardinal features of SIAD were described by Bartter and Schwartz (Fig. 5.22). These criteria must be fulfilled before a diagnosis of SIAD can be made. The measurement of plasma vasopressin does not aid the diagnosis of SIAD because over ninety per cent of all patients with hyponatraemia, irrespective of their extracellular volume status or underlying cause, have detectable or elevated vasopressin concentrations.
