Solute loss plays a major role in polydipsia-related hyponatraemia of both water drinkers and beer drinkers

Abstract

Background: Polydipsia-related hyponatraemia is generally considered an acute dilutional state. Aim: To determine whether solute loss plays a role in the pathogenesis of polydipsia-related hyponatraemia. Design: Prospective uncontrolled study Methods: We studied routine biochemical volume-related parameters before and after 2l isotonic saline infusion over 24h, in 10 consecutive hyponatraemic polydipsia patients (mean age 55 ± 11 years; 6 beer drinkers and 4 compulsive water drinkers) with initial urinary osmolality <220 mosm/kg H2O. In five of these patients, we measured balance data over 24h. Results: Mean initial plasma protein concentration in the 10 studied polydipsia patients was 7 ± 0.7 g/dl, unexpectedly high for an acute dilutional state. Mean plasma sodium concentration increased from 126 ± 5 mmol/l before saline, to 135 ± 5 mmol/l after infusion of 2 l isotonic saline (p < 0.01). Balance data in five polydipsia patients showed a mean decrease of 1.6 kg of their initial body weight and a mean salt retention of 406 mosm. Discussion: Polydipsia-related hyponatraemia is a mixed disorder, in which about half of sodium decrease is due to solute loss. This explains the apparent paradox of a normal plasma protein concentration, despite the increase in body weight due to water intoxication.