Effects of maintenance lithium treatment on serum parathyroid hormone and calcium levels: a retrospective longitudinal naturalistic study

OBJECTIVE: The aim of this retrospective longitudinal naturalistic study was to evaluate the effects of maintenance lithium treatment on parathyroid hormone (PTH) and calcium levels. METHODS: A retrospective longitudinal naturalistic study design was used. Data were collected from the database of a tertiary psychiatric center covering the years 2010–2014. Included were bipolar patients who had never been exposed to lithium and had lithium started, and who had PTH, and total and ionized calcium levels available before and during lithium treatment. Paired t-tests were used to analyze changes in PTH and calcium levels. Linear regressions were performed, with mean lithium level and duration of lithium exposure as independent variables and change in PTH levels as dependent variable. RESULTS: A total 31 patients were included. The mean duration of lithium treatment was 18.6±11.4 months. PTH levels significantly increased during lithium treatment (+13.55±14.20 pg/mL); the rate of hyperparathyroidism was 12.9%. Neither total nor ionized calcium increased from baseline to follow-up; none of our patients developed hypercalcemia. Linear regressions analyses did not show an effect of duration of lithium exposure or mean lithium level on PTH levels. CONCLUSION: Lithium-associated stimulation of parathyroid function is more common than assumed to date. Among parameters to be evaluated prior to lithium implementation, calcium and PTH should be added.