Objectives:
The aim of the present study was to compare blood serum kynurenic acid (KYNA) concentrations measured before ECT and after 1, 6 and 12 electroconvulsive treatment (ECT) sessions in patients with diagnoses of recurrent depressive disorder (RDD), depression in bipolar disorder (DBD) and schizoaffective disorder (SAD).

Methods:
The study group comprised of 50 patients with ICD-10 diagnoses of RDD, DBD and SAD. Blood serum KYNA concentrations were determined and clinical assessment was performed using the MADRS and the GAF scale.

Results:
Significant differences were found in blood serum KYNA levels between RDD, DBD and SAD patients treated with electroconvulsive therapy and healthy controls: 1) KYNA concentrations in DBD patients measured before ECT and after 12 ECT sessions were significantly lower than in the control group; 2) KYNA concentrations in the serum of RDD patients measured before ECT and after one and 12 ECT sessions were significantly lower than in the control group, while those measured after 6 ECT session did not differ significantly from KYNA concentrations in healthy controls; 3) higher pre-treatment blood serum concentrations of KYNA in DBD patients correlated with a higher number of illness phases and poorer general functioning before treatment; 4) significant relationships were found between higher blood serum concentrations of KYNA in RDD patients after 1 ECT session and male gender, and between higher KYNA concentrations after 6 ECT sessions and increased depression and poorer functioning before treatment in those patients.

Conclusions:
Results show that KYNA concentrations in all diagnostic groups were lower before ECT (not statistically significant for the SAD group) and that there were no significant changes in those concentrations (compared with the baseline) during ECT.