Hypercalcaemia, hyperparathyroidism, and their associated factors among lithium users in a psychiatric clinic in Hong Kong.

Objectives: To investigate the prevalence of hypercalcaemia and its associated factors among Chinese lithium users in a psychiatric clinic in Hong Kong.

Methods: Chinese outpatients aged ≥18 years who were treated with lithium and followed up at the Department of Psychiatry, Kowloon Hospital, between 1 September 2023 and 30 June 2024 were identified. Eligible patients were interviewed, and their medical records were reviewed. Blood tests for renal and thyroid functions, estimated glomerular filtration rate, and levels of serum calcium, albumin, and lithium were ordered. A blood test for serum lithium levels was typically taken 12 hours after lithium use. In patients with hypercalcaemia, an additional blood sample was taken to measure parathyroid hormone and vitamin D levels. Multivariable logistic regression analysis was performed to identify risk factors for hypercalcaemia.

Results: Of 238 patients included, 48 (20.2%) had hypercalcaemia, of whom eight (16.7%) also had hyperparathyroidism. Hypercalcaemia was independently associated with diabetes mellitus (adjusted odds ratio [AOR] = 2.89, p = 0.011), cumulative duration of lithium use (AOR = 1.08, p < 0.001), and serum lithium levels (AOR = 5.45, p = 0.048).

Conclusion: Lithium-associated hypercalcaemia and hyperparathyroidism are often undetected. When left unmanaged, these conditions can lead to cardiovascular mortality, cerebrovascular impairment, and premature death. Therefore, calcium levels should be regularly monitored, particularly in patients with diabetes mellitus, a longer cumulative duration of lithium use, and higher serum lithium levels.