Objectives: We investigated the association between serum levels of C-reactive protein (CRP), a marker of inflammation, and the severity of psychopathology in outpatients with bipolar disorder. We also compared the levels of CRP in the bipolar disorder individuals with those of a non-psychiatric control group.
Methods: We measured the level of CRP in N=122 outpatients with bipolar disorder and N=165 control individuals and evaluated the symptom severity of the bipolar disorder patients with the Young Mania Rating Scale (YMRS) and the Hamilton Depression Scale (Ham-D).
Results: Within the bipolar disorder sample, CRP was significantly associated with the YMRS score (r=.306, p<.006), age of onset, gender, and race. CRP was not significantly associated with the Ham-D score or other clinical or demographic variables. In a multivariate analysis of covariance, CRP was the only independent predictor of YMRS score (F=11.7, p=.0009). The CRP levels of the n=41 individuals with YMRS >6 were significantly greater than the levels of the n=81 individuals with YMRS <or=6 (F=7.94, <.006). The CRP levels of the group with YMRS >6 were also significantly greater than the levels of the control group (p=.033) while the CRP levels of the group with YMRS <or=6 did not differ from that of controls (p>.05).
Conclusions: Our results suggest that outpatients with bipolar disorder with mania symptoms have increased levels of CRP as compared to those without mania symptoms and compared to individuals without psychiatric disorders. The long-term consequences of CRP in bipolar disorder should be the subject of future studies.