Objectives:
The aim of the study was to assess concentrations of the following neuropeptides: phoenixin, spexin and kisspeptin in venous blood serum of children and adolescents suffering from bipolar disorder, and by this their predictive efficiency in this disorder.

Methods:
The study covered 75 individuals with a mean age of 15.26 years (95% CI: 14.86–15.67), of which the study group comprised of 57 individuals diagnosed with bipolar affective disorder and the control group – 18 individuals with no psychiatric diagnosis and no pharmacological treatment. Phoenixin, spexin and kisspeptin levels were determined in the peripheral venous blood serum. Neuropeptide concentrations were measured with the enzyme-linked immunosorbent assay (ELISA).

Results:
The mean phoenixin concentration in the studied group equalled 1.57 ng/ml (95% CI: 1.35–1.79), while in the control group – 2.69 ng/ml (95% CI: 2.38–3; U Mann-Whitney test p-value < 0.05). For spexin, these results were 639.65 pg/ml (95% CI: 558.86–720.44) in the studied group, and 354.28 pg/ml (95% CI: 310.33–398.22; U Mann-Whitney test p-value < 0.05) in the control group. The observed differences were statistically significant. The mean concentration of kisspeptin levels in the studied group was 126.02 pg/ml (95% CI: 39.82–212.23; median: 59.85), while in the control group – 54.83 pg/ml (95% CI: 39.23–70.43; median: 51.3; U Mann-Whitney test p-value = 0.29), and the observed difference was not statistically significant.

Conclusions:
The occurrence of bipolar disorder symptoms is statistically significantly linked with a decreased phoenixin concentration and to a small degree – with an increased spexin concentration in blood serum of patients. However, it is not linked with the kisspeptin concentration.