"CRP [C-reactive protein] concentrations are increased in bipolar disorder regardless of mood state, but are higher during mania than in depression and euthymia, suggesting an increased inflammatory burden in mania."
So said the systematic review and meta-analysis published by Brisa Fernandes and colleagues  who surveyed the peer-reviewed literature on the topic of "measured serum and plasma CRP concentrations in adult patients with bipolar disorder (as defined by DSM-IV-TR) and healthy controls" and arrived at their conclusions based on an analysis of some 2000 people diagnosed with bipolar disorder (BD). CRP by the way, a member of the pentraxin family, is the molecule of choice when it comes to looking at response to inflammation. BD, previously known as manic depression, is a condition characterised by periods of depression and mania.
Continuing an important theme in psychiatry - that the immune system or expression of the immune system whether in terms of genetics or biology, seems to show some important associations with behaviour (see here for example) - the Fernandes paper represents important work. Of course it's not the first time that CRP levels and bipolar disorder have been mentioned on this blog (see here) but the 'collecting' of results based on the use of systematic review and meta-analysis this time around strengthens the association between these variables.
Where next I hear you ask? Well, the idea that CRP levels might be linked to cases of BD needs further research not least to ensure that certain over-represented medical comorbidity linked to BD are not an interfering variable when it comes to CRP levels (see here). The findings should also perhaps be seen in a larger context where CRP levels have been reported in other psychiatric / behavioural labels (see here). The non-specificity of CRP (i.e. not tied to just one label) also has implications for the idea that many different psychiatric / behavioural labels might show overlapping features (see here) for example.
With no medical or clinical advice given or intended, there is also the intriguing idea that interventions targeting specific immune function findings may also have behavioural implications (see here for example). This alongside the idea that some medicines intended for the treatment or management of aspects of BD may already have some 'immune-modulating' actions (see here) potentially tied into their potential efficacy (or not). Again, further research is very much implied.
 Fernandes BS. et al. C-reactive protein concentrations across the mood spectrum in bipolar disorder: a systematic review and meta-analysis. Lancet Psychiatry. 2016 Nov 9. pii: S2215-0366(16)30370-4.
Fernandes BS, Steiner J, Molendijk ML, Dodd S, Nardin P, Gonçalves CA, Jacka F, Köhler CA, Karmakar C, Carvalho AF, & Berk M (2016). C-reactive protein concentrations across the mood spectrum in bipolar disorder: a systematic review and meta-analysis. The lancet. Psychiatry PMID: 27838212