Serum osmolarity in male patients with bipolar disorder manic episode

NEW FINDINGS: What is the central question of this study? The main goal of this study was, for the first time, to investigate the role of the serum osmolarity in bipolar disorder manic episode. What is the main finding and its importance? Our results demonstrate a diminished serum osmolarity in manic episode compared with healthy control subjects. This finding supports the hypothesis of a fluid and electrolyte imbalance during acute episodes. Decreased serum osmolarity might be a reflection of a relative haemodilution in mania. Imbalance of water and electrolyte homeostasis has been suggested to be associated with acute episodes of bipolar disorder. In this study, we aimed to investigate, for the first time, the serum osmolarity in bipolar disorder manic episode. A total of 68 bipolar inpatients in manic episode and 60 age- and sex-matched healthy control subjects were included in the study. Serum osmolarity was calculated from sodium (Na+ ), glucose and blood urea nitrogen (BUN) according to following formula: (2 × Na+ ) + (BUN/2.8) + (glucose/18). The significance level was accepted as P < 0.05. The serum osmolarity of manic patients was 295.34 ± 4.90 mosmol/l and that of the control group was 298.46 ± 5.33 mosmol/l. The serum osmolarity of the manic group was significantly lower than that of control subjects (P < 0.001). When we compared the components of serum osmolarity, a statistically significant difference was also observed between groups in terms of glucose (85.85 ± 12.25 mg/dl for manic, 92.95 ± 20.77 mg/dl for control subjects, P = 0.019) and Na+ (140.73 ± 2.06 mmol/l for manic, 142.06 ± 2.48 mmol/l for control subjects, P = 0.001). For BUN concentrations, there was no statistically significant difference between manic (25.50 ± 9.85 mg/dl) and control (26.61 ± 6.64 mg/dl) groups (P = 0.461). Our results demonstrate a diminished serum osmolarity in manic episode compared with healthy control subjects. This finding supports the hypothesis of a fluid and electrolyte imbalance during acute episodes. Decreased serum osmolarity might be a reflection of a relative haemodilution in mania. However, exploration of the role of fluid and electrolyte homeostasis and mechanisms of related hormones may contribute to a better understanding of the aetiology of bipolar disorder.