There are two possible approaches to the diagnosis of hyponatremia: the classical method and the "lazy man's method". Both are offered here. In their most basic form, the approaches require essentially the same tests (serum osmolality, urine osmolality and urinary sodium). In the classical method, one is expected to examine the patient and come to a conclusion regarding their fluid status. The lazy man will of course do no such thing, as it requires for him to get up. Instead, the examination of the patient is deferred until the absolute last moment, and consists of deciding whether the patient has SIADH or cerebral salt wasting on the basis of their volume status and urine output.