Inflammatory processes and neural-immune interactions have been implicated in the pathogenesis of psychiatric conditions, but studies in bipolar disorder are inconclusive so far. The purpose of this study was to investigate whether peripheral concentrations of C-reactive protein, an acute-phase response protein of inflammatory activity, are increased in bipolar disorder across the mood spectrum.

Meta-analyses were performed comparing C-reactive protein concentrations in patients in mania, depression, or euthymia, with those in healthy controls, and two within-group meta-analyses compared changes in concentrations before and after treatment of an index manic or depressive episode.

C-Reactive protein concentrations were increased in bipolar disorder regardless of mood state, but were higher during mania than in depression and euthymia, suggesting an increased inflammatory burden in mania. The extent of the concentration increases in mania and depression was not related to symptom severity.

.Fernandes BS, Steiner J, Molendijk ML, Dodd S, Nardin P, Gonçalves CA, Jacka F, Köhler CA, Karmakar C, Carvalho AF, Berk M: C-reactive protein concentrations across the mood spectrum in bipolar disorder: a systematic review and meta-analysis. Lancet Psychiatry 3(12):1147-1156 (2016).

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https://www.ncbi.nlm.nih.gov/pubmed/27838212