N Ruljančić¹ , A Bronić² , D Rogić³

¹Psychiatric hospital «Sveti Ivan», Laboratory of Medical biochemistry, Jankomir 11, 10000 Zagreb, Croatia, ²University hospital of traumatology, Department of laboratory diagnostics, Draškovićeva 19, 10000 Zagreb, Croatia, ³Clinical Hospital Center Zagreb, Clinical Institute of laboratory diagnostics, Kišpatićeva 12, 10000 Zagreb, Croatia

AIM
To determine the concentration of total blood magnesium (tMg) and ionized magnesium (iMg) in serum of patients with bipolar disorder treated by maintenance therapy lithium carbonate (1,2).

METHODS
The concentration of tMg was measured by spectrophotometric method (reference interval 0,70 mmol/l – 1,10 mmol/l) while the concentration of iMg was measured by ion-selective electrodes (reference interval 0,53 mmol/l-0,67 mmol/l). Serum of 33 patients, 30 women and 3 men,aged between 26 and 53 was tested. All of our patients were in maintenance therapy interval (0,60-1,2 mmol/l). The concentration of lithium carbonate in the serum was measured by flame photometry.

RESULTS
In all patients the obtained concentration of tMg ranged from 0,79 mmol/l to 1,02 mmol/l (average level 0,90 mmol/l) and the concentration of iMg ranged from 0,53mmol/l to 0,77 mmol/l (average level 0,61 mmol/l). iMg in 25/33 patients was in reference interval while higher blood levels of iMg (higher then 0,67mmol/l) were seen in 7/33 patients.

CONCLUSION
Our results show that normomagnesemia measured as tMg is a common finding in patients with bipolar disorder, but when measured as iMg, about 21% patients no longer show to be normomagnesemic. This findings imply that the measurement of iMg is preferred above the routinely measured tMg.

REFERENCE
1. Kirov GK, Bisch NJ, Steadman P, Ramsey RG. Plasma magnesium levels in a population of psychiatric patients: correlations with symptoms. Neuropsychobiology. 1994;30(2-3):73-8
2. Widmer J, Bovier P, Karege F, Raffin Y, Hilleret H et al. Evolution of blod magnesium, sodium and potassium in depressed patients followed three months. Neuropsychobiology. 1992;26(4):173-9