Hyponatremia and In‐Hospital Falls and Fractures in Older Adults

To the Editor: Falls are a substantial cause of morbidity and mortality in US hospitalized older adults with an estimated prevalence of 3.56 falls per 1000 patient-days, 26% of which result in injury. In-hospital falls contribute to fractures causing lengthier hospitalizations, costlier care, and increased mortality. Falls represent a leading indicator of quality of hospital care, compelling institutions to establish fall prevention programs including risk assessment and targeted interventions. Multiple fall risk assessment tools have been introduced, such as the Johns Hopkins Fall Risk Assessment Tool, Morse Fall Scale, STRATIFY, Hendrich II Fall Risk Model, Fall Risk Assessment Tool (FRAT), and Stopping Elderly Accidents, Deaths and Injuries (STEADI). These tools incorporate various patient characteristics including age, sex, fall history, cognition, functional status, and medications. A meta-analysis of 33 studies revealed that available assessment tools do not sufficiently predict fall risk among older adults, and combining two such tools is recommended to augment predictability. On reviewing the risk assessment instruments just cited, we were struck by the universal omission of an important predisposing condition to falls, namely hyponatremia. Hyponatremia is the most common electrolyte abnormality encountered in hospitalized patients, with an estimated prevalence on the order of 30%. It was associated with a longer hospital length of stay, increased risk of discharge to a shortor long-term facility, higher in-hospital mortality, increased risk of readmission, and costlier care of up to $3000 higher per patient. Previously viewed as asymptomatic, even mild chronic hyponatremia is now strongly associated with several adverse outcomes including falls, fractures, andmortality. A meta-analysis of 15 studies revealed an association of hyponatremia with falls and fractures. The original study investigating the association between falls and hyponatremia estimated an adjusted odds ratio of 67 for admission to the hospital with falls in hyponatremic older adults comparedwith normonatremic controls. The association of hyponatremia with falls is stronger for hospitalized patients than community dwellers. Several putative mechanisms have been proposed for the increased risk of falls and fractures in chronic hyponatremia. Evenmild chronic hyponatremia induces reversible gait instability and neurocognitive deficits, possibly through reduction of the neurotransmitter glutamate during brain adaptation to chronic hyponatremia. A clinical study including more than 5000 community-dwelling men aged 65 years and older revealed that hyponatremia is associated with cognitive impairment. Further, several clinical studies have established an association between chronic hyponatremia and osteoporosis. Experimental work in the rat demonstrated that chronic hyponatremia reduces bone mineral density with both trabecular and cortical bone loss secondary to enhanced osteoclastic activity and decreased osteoblastic activity. The decreased osteoblastic activity results in reduced serum osteocalcin, a biomarker of bone formation. Additional work in cell cultures demonstrated that low extracellular sodium concentration directly stimulates osteoclast formation and resorptive activity, mimicking the effects of chronic hyponatremia. These changes may bemediated by increased oxidative stress in bone aiming to mobilize its sodium stores. The strong association of chronic hyponatremia with falls and fractures in older adults is well documented. Furthermore, both hyponatremia and falls are independently associatedwith heightened morbidity and mortality. They also constitute an increased economic burden and adversely impact hospitalization costs. On the basis of this evidence, we propose inclusion of hyponatremia, regardless of severity, in all fall risk assessment tools for hospitalized older adults.