Abstract
Hyponatraemia is a common electrolyte disturbance, with moderate (serum sodium: 125–129 mmol/L) to severe (serum sodium: ≤125 mmol/L) forms of the disease occurring in 4–15% of hospitalised patients. While it is relatively common, determining the underlying cause of this condition can be challenging and may require extensive laboratory investigations. To this end, it is important to ascertain the efficacy of laboratory tests in determining the cause of hyponatraemia. Up to 10% of patients with hypothyroidism also have hyponatraemia. Routine evaluation of thyroid function is often advocated in cases of low serum sodium. A review and discussion of the available literature is presented here to examine this recommendation.