Polydipsia in chronic psychiatric patients. Body weight and plasma sodium.

Eight chronic psychiatric in-patients with polydipsia, and polyuria, up to 22 litres per 24 hours, were studied by frequent timed body weight and urine volume measurements, and episodic plasma electrolyte estimations. During the day they all showed irregular water retention, with hyponatremia in proportion to the weight gain. During the night they always lost water and weight, returning to their individual lowest weights and to normal plasma sodium. Measurement of weight in chronic psychiatric patients can be used to identify patients with significant polydipsia, to monitor those with the disorder and permit targeted fluid restriction, and to assess the efficacy of treatment procedures such as medication.