This retrospective cohort study examined Hospital Episode Statistics (HES) and Hospital Pharmacy Audit (HPA) data from 41 hospital trusts to understand how hyponatraemia secondary to syndrome of inappropriate antidiuretic hormone secretion (SIADH) is currently treated in England, and to understand the associated resource use. Hyponatraemia is the electrolyte disturbance that is most commonly encountered in clinical practice (affecting 1030% of hospitalised patients), with SIADH a common cause; responsible for about 30% of patients with hyponatraemia. After application of inclusion/exclusion criteria, 3,060 patients had a robust diagnosis of SIADH. Of these patients, 927 were treated with demeclocycline, 120 were treated with tolvaptan and 2013 had no pharmacological treatment for SIADH recorded, which may mean they had fluid restriction, saline administration or received no treatment. Treatment with tolvaptan was associated with a shorter length of hospital stay, lower inpatient costs and fewer subsequent A&E attendances than treatment with demeclocycline. Demeclocycline treatment was associated with fewer outpatient attendances than tolvaptan treatment. Patients who had no recorded pharmacological treatment had lower inpatient costs, but more outpatient appointments and A&E attendances than those given either demeclocycline or tolvaptan. This study showed a significant discrepancy between reported incidence of hyponatraemia/SIADH and the number of patients given appropriate clinical codes for these conditions. A code for hyponatraemia was present in 59 661 out of 3 508 638 patients (1.7%), and 8.9% of these had a code for SIADH. This level of under-reporting has potentially serious implications for hospital remuneration.
This study shows that hyponatraemia secondary to SIADH represents a substantial and under-reported healthcare burden in England. Management of SIADH is variable, but treatment with tolvaptan could potentially result in lower resource usage for hospitals and the wider health economy than treatment with demeclocycline.