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Intern Med J. 2007 Mar;37(3):149-55.

Risk factors for symptomatic hyponatraemia: the role of pre-existing asymptomatic hyponatraemia.

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Department of Internal Medicine, Division of Nephrology, University of Virginia Health System, Charlottesville, Virginia, USA.



Hyponatraemia is associated with substantial morbidity and mortality. Identification of the risk factors associated with the development of symptomatic hyponatraemia is important in determining preventive strategies.


A retrospective analysis of the risks factors associated with the development of severe, symptomatic hyponatraemia requiring hospital admission over the past 3 years at our institution was carried out.


Forty-seven patients (26 women, 21 men) with a hospital admission serum sodium <134 mmol/L were identified. Of these patients, 31 (65.9%) had associated changes in the mental status that improved with the treatment of the hyponatraemia suggesting causality. The average admission sodium level of this cohort was 118.8 mmol/L. Symptomatic hyponatraemia was associated with volume depletion (32.6%), congestive heart failure (26%), syndrome of inappropriate antidiuretic hormone (26%), thiazide diuretic use (26%) and selective serotonin re-uptake inhibitor use (26%). In 21.7% of cases, the cause was multifactorial (congestive heart failure, syndrome of inappropriate antidiuretic hormone or medication use with volume depletion). In 11% of cases, patients were taking both thiazide diuretics and serotonin re-uptake inhibitors. Most importantly, 70.9% of all patients admitted with symptomatic hyponatraemia had pre-existing hyponatraemia that was untreated and believed to be asymptomatic (P < 0.05). This was the most common risk factor identified. We next investigated the prevalence of presumed asymptomatic hyponatraemia in the outpatient setting. Out of 27 496 patients analysed, 14% had serum sodium levels less than or equal to 134 mEq/L and 4% had values less than 130 mEq/L.


Pre-existing asymptomatic hyponatraemia is a common finding and is associated with a high risk for the development of worsening hyponatraemia with altered mental status.

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