Age and gender as risk factors for hyponatremia and hypernatremia
Introduction
There is little agreement on the prevalence of disturbances of sodium balance or on the importance of gender and age as markers of risk. Previous estimates of hyponatremia of 0.2–29.8% [1], [2] and hypernatremia of 0.3–8.9% [3], [4] have varied with the differences in the definitions of the disturbance and the population surveyed. Most studies on hyponatremia have examined elderly and/or psychiatric populations with particular emphasis on psychotropic medications as a cause of hyponatremia [5], [6]. Little has been published on the comparative prevalence of hypo- and hypernatremia in different patient populations (hospital or community). Female gender has been suggested as a risk factor for psychotropic [7], diuretic [8], and exercise-induced [9] hyponatremia. While some studies show increasing age to be a risk factor [7], others show no association with age [8], [10]. This study assesses gender and age as independent risk factors for hypo- and hypernatremia in a mixed community/hospital population and describes the prevalence of different levels of dysnatremia (hyponatremia and hypernatremia) in different population groups.
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Materials and methods
Tan Tock Seng Hospital Biochemistry Laboratory services a 1200-bed acute care hospital and its attendant outpatient services, and three community-based primary care polyclinics. All patients are admitted to the hospital via the emergency department. Serum Na measurements are performed on two Roche 917 clinical chemistry analysers using indirect ion-selective electrode technology. A 95% reference interval of 136–145 mmol/l was established in 1999 based on 560 normoglycemic multiphasic health
Results
Over the 2-year period, 306,140 samples were analysed for serum Na, of which 303,577 samples (120,137 patients) had age, gender, and location recorded. The average age was 55 years with 43% aged >60 years and 23% aged >70 years. A total of 36% (average age 53.4 years) of patients were from acute hospital care (inpatient and emergency department), 44% (53.8 y) from ambulatory hospital care (outpatient), and 20% (59.6 years) from community-based care (polyclinics).
The prevalence of dysnatremia in
Discussion
These results provide quantification of the prevalence of dysnatremia in different populations, confirming hyponatremia as a common but generally mild condition, which is often present on admission [12], and hypernatremia as uncommon and usually developing after admission [4]. Inspection of the few comparable prevalence figures published suggest similar rates might be seen in Western populations. Miller et al. found a hyponatremic preva1ence of 18% in nursing home residents >60 years (similar
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