title: Hypercalcemia in patients with bipolar disorder treated with lithium: a cross-sectional study.
abstract: BACKGROUND
  Lithium-induced hyperparathyroidism (LIH) is a relative underrecognized complication of long-term lithium treatment. Hypercalcemia may be the first, but often overlooked, sign of LIH. Symptoms of LIH can be similar to the underlying psychiatric illness, which may cause a significant doctor's delay in diagnosing LIH. The aim of this study was to determine the prevalence of hypercalcemia in a cohort of psychiatric patients.
  
  
  METHODS
  In this cross-sectional study, we collected data from 314 patients treated with lithium in an outpatient clinic for bipolar disorder. Patients with bipolar disorder from the same clinics, who had never been treated with lithium and of whom serum calcium levels were available, were included as controls (n = 15). Patient characteristics and laboratory results were collected during the period of June 2010 till June 2011.
  
  
  RESULTS
  The mean serum calcium level was 2.49 (SD 0.11) mmol/l. The point prevalence of hypercalcemia (>2.60 mmol/l) was 15.6%. In a comparable group of psychiatric patients not using lithium, the mean serum calcium level was 2.37 mmol/l, and none of these patients had hypercalcemia (p = 0.001). The duration of lithium treatment was the only significant predictor for the development of hypercalcemia (p = 0.002).
  
  
  CONCLUSIONS
  The prevalence of hypercalcemia in lithium-treated patients was significantly higher than that in non-lithium treated controls and correlated to the cumulative time lithium was used in this cross-sectional study. We recommend that serum calcium levels should be routinely tested in patients using lithium for timely detection of LIH or hypercalcemia due to other causes.
authors.affiliation: Department of Surgery, University Medical Center Utrecht, Huispostnummer G04.228, P.O. Box 85500, Utrecht, 3508GA the Netherlands.
authors.forename: Bas A
authors.initials: BA
authors.lastname: Twigt
authors.affiliation: Department of Surgery, University Medical Center Utrecht, Huispostnummer G04.228, P.O. Box 85500, Utrecht, 3508GA the Netherlands.
authors.forename: Bernard M
authors.initials: BM
authors.lastname: Houweling
authors.affiliation: Department of Surgery, University Medical Center Utrecht, Huispostnummer G04.228, P.O. Box 85500, Utrecht, 3508GA the Netherlands.
authors.forename: Menno R
authors.initials: MR
authors.lastname: Vriens
authors.affiliation: Altrecht Institute for Mental Health Care, Lange Nieuwstraat 119, Utrecht, 3512 PG the Netherlands.
authors.forename: Eline J
authors.initials: EJ
authors.lastname: Regeer
authors.affiliation: Altrecht Institute for Mental Health Care, Lange Nieuwstraat 119, Utrecht, 3512 PG the Netherlands ; Department of Psychiatry, VU University Medical Center, De Boelelaan 1117, Amsterdam, 1081HV the Netherlands.
authors.forename: Ralph W
authors.initials: RW
authors.lastname: Kupka
authors.affiliation: Department of Surgery, University Medical Center Utrecht, Huispostnummer G04.228, P.O. Box 85500, Utrecht, 3508GA the Netherlands.
authors.forename: Inne Hm Borel
authors.initials: IH
authors.lastname: Rinkes
authors.affiliation: Department of Endocrinology, University Medical Center Utrecht, Heidelberglaan 100, Utrecht, 3583CX the Netherlands.
authors.forename: Gerlof D
authors.initials: GD
authors.lastname: Valk
keywords: Bipolar disorder; Hypercalcemia; Lithium; Lithium-induced hyperparathyroidism