Prevalence, Incidence and Etiology of Hyponatremia in Elderly Patients with Fragility Fractures

INTRODUCTION Hyponatremia (serum sodium<135 mMol/L) is the commonest electrolyte imbalance encountered in clinical practice. It is associated with multiple poor clinical outcomes including increased mortality, longer hospital stay, falls and fractures. Prevalence is higher in frail patient groups, and elderly patients with fragility fractures (EPFF) are particularly susceptible. Euvolemic hyponatremia due to syndrome of inappropriate anti-diuretic hormone (SIADH) is widely assumed to be the commonest cause. However, little is known about the epidemiology and etiology of hyponatremia in EPFF. This study established prevalence, incidence and etiology of hyponatremia in EPFF. METHODS Prospective observational study of consenting adults aged ≥65 years admitted with a fragility fracture to a university hospital between 7th January and 4th April 2013. Prevalence of hyponatremia on admission and incidence of cases developing in hospital were reported. Etiology of cases of hyponatremia was determined by consensus of an expert panel using pre-specified data collected daily. RESULTS 127/212 (60%) EPFF were recruited (mean age 79 yrs, 78% female). Two participants withdrew mid-study. Of those not recruited, 66 had incapacity to consent and 19 refused participation. Point prevalence of hyponatremia on admission was 13.4% and a further 12.6% developed hyponatremia during admission. Hypovolemic hyponatremia was predominant (70%). 73% of cases were multi-factorial in etiology. The commonest potentially causative factors in cases of hyponatremia were thiazide diuretics (76%), dehydration (70%), proton pump inhibitors (70%), SIADH (27%) and mirtazapine (15%). CONCLUSION Hyponatremia is highly prevalent in EPFF, seen in 26% of cases. Dehydration and prescription of thiazide diuretics and proton pump inhibitors were the commonest potentially causative factors, not SIADH.