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Hyponatraemia in the Older Patient – a Case-control Study

Hyponatraemia is a common electrolyte disturbance occurring in the elderly with associated morbidity and mortality. Diagnosis and management of hyponatraemia can be complex, especially in the elderly due to polypharmacy, comorbidities and endocrinopathies. A retrospective observational case-control study has been conducted in the geriatric ward (≥65 years) over a 24-month period to assess the prevalence and risk factors for hyponatraemia. Control patients (Na 135 – 145 mmol/L) were matched in a 1:1 ratio on volume status, age (±5 years), gender and similar comorbidities with hyponatraemia patients (Na <130 mmol/L).


Hyponatraemia can result in significant morbidity such as headaches, confusion, seizures, coma and death

(1-3). Clinical presentations of hyponatraemia are variable and depend on the severity of depletion and abruptness of onset (2, 3). Clinical symptoms usually appear when serum sodium concentration is below 130 mmol/L; mortality rate is high when serum sodium concentration is below 120 mmol/L (2,3). With increasing polypharmacy and comorbidities in an aging population, the prevalence of hyponatraemia is likely to continue to rise. Understanding the prevalence and risk factors will aid in de-prescribing causative agents and improve health status by effectively treating comorbidities and endocrinopathies.


Hyponatraemia can occur in hypovolaemia, euvolaemia and hypervolaemia. Knowing the patients fluid status can aid in determining the cause of hyponatraemia (5, 8). Hypovalaemic hyponatraemia can occur from gastrointestinal loss (diarrhoea, vomiting), loss of sodium through the skin (burns, excessive sweating), renal sodium loss (diuretics) and poor water intake (5,8). Euvolaemia hyponatraemia can occurs in syndrome of inappropriate secretion of antidiuretic hormone (antiepileptics, psychotropic drugs), adrenal insufficiency, inappropriate intravenous fluid (enough water, not enough sodium), and primary psychogenic polydipsia (1-7). Hypervolaemic hyponatraemia can occur on congestive cardiac failure, cirrhosis, myxoedema, nephrotic syndrome, inappropriate intravenous fluids (too much water, not enough sodium), and drugs (NSAIDs, corticosteroids, fludrocortisone) (5, 8).

The objective of this study is to determine the prevalence and risk factors for hyponatraemia in elderly patients assessing their medications, comorbidities and endocrinopathies for cause.

Study design:


A retrospective observational case-control study design was used to assess the prevalence and relationship between medications, comorbidities and endocrinopathies and the occurrence of hyponatraemia. Case and control patients were selected from the geriatric ward on admission, over a 24-month period. Subjects were excluded is they were younger than 65 years of age.  Patient laboratory data, medication history and medical history were examined.


Exposed group

Cases included all individuals admitted to the geriatric ward who experienced at least one period of hyponatraemia within the study period, irrespective if they were symptomatic or asymptomatic. Hyponatraemia was defined as serum sodium concentrations of ≤130 mmol/L. Patients were stratified into hypovalaemic, euvolaemic and hypervolaemic. Cases were counted only once even if they experienced more than one episode of hyponatraemia during the study period.

Unexposed group

Control subjects were matched to a 1:1 ratio to case subjects with similar volume status, age (±5 years), gender and similar comorbidities. Control subjects were defined as those patients with a sodium serum concentration between 136 mmol/L and 144 mmol/L. Subjects with a sodium concentration between 131 mmol/L and 135 mmol/L were excluded to eliminate subclinical hyponatraemia and to ensure a clear contrast between cases and controls.

Primary endpoint

The objective of this study is to determine the prevalence and risk factors for hyponatraemia in elderly patients.

Secondary endpoint

Assessing which agents were more likely to cause hyponatraemia: medication, comorbidities or endocrinopathies.

Outcome status of patient on discharge from ward i.e. resolved hyponatraemia, unresolved hyponatraemia, morbidity or mortality.



Confounders in this study included volume status, age, gender and comorbidities. These were taken into account when matching cases and controls to a 1:1 ratio*. Subjects were matched on their volume status (reduced, normal or increased), age (±5 years), gender and comorbidities. Subjects were restricted to over 65 years of age, irrespective of their presence on the ward (i.e. outliers) and serum sodium concentration. Once the data was pooled, subjects were further stratified into hypovolaemia, euvolaemia, and hypervolaemia to further analyse the possible causation of hyponatraemia.

*It is important to note that cases and controls, which could not be matched to all four variables, were matched on a minimum of two variables.

Statistical analysis

For both cases and controls the prevalence of polypharmacy, comorbidities and endocrinopathies were determined. A t-test was used to assess the significance of differences in the mean of variables between the cases and controls. Chi-square test was used to test for the significance of the variables. To estimate the association between medication, comorbidities and endocrinopathies with hyponatraemia, odds ratio and adjusted odds ratio with 95% confidence intervals were calculation using logistic regression. Stratified analysis was used to further determine causation. All statistical calculation was carried out using SPSS statistical package.

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Bias limitation
In order to reduce selection bias, all subjects who were admitted to the geriatric ward over a 24-month period were enrolled into the study. Only patients who were less than 65 years were excluded from the study.

Patient laboratory data, medication history and medical history examined were blinded to the study team. Standardised data points were collected for each subject e.g serum sodium concentration, serum creatinine, fluid balance, medication history. This was to reduce measurement bias.

Subjects with a sodium concentration between 131 mmol/L and 135 mmol/L were excluded and could potentially have subclinical hyponatraemia. However, their data was not collected, as it was essential to be able to clearly define hyponatraemia and eunatremia.

Limitations of our study include possible small numbers of patients identified on the geriatric ward with hyponatraemia. This could be due to potential subjects who are ≥65 years not being admitted onto the geriatric ward, rather they could be admitted under other treating teams depending on their presentation for instance gastrointestinal, neurology or ICU. This limitation was reduced as the data was collected over a 24-month period, to aid in recruiting a significant proportion of subjects.


Hyponatraemia is a potentially serious medical condition in the elderly, which can impact their morbidity and mortality. With increasing polypharmacy, comorbidities and endocrinopathies in our aging population, the prevalence of hyponatraemia is likely to continue to rise. This study aims to assess the prevalence and risk factor for hyponatraemia which can be used to de-prescribe causative agents in the elderly, improve health status and effectively treat comorbidities and endocrinopathies.



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