Does CRP predict outcome in bipolar disorder in regular outpatient care?

Background: The association between inflammation and the course of mood disorders is receiving increased attention. This study aims to investigate whether a sub-group of patients with BD can be identified for which a higher CRP (C-reactive protein) level at baseline is associated with an unfavorable prognosis.

Methods: This is a historic cohort study using CRP at baseline, with 15-month follow-up of mood status and medication. Cross-sectional analyses include boxplots, one-way ANOVA, receiver operating characteristics (ROC) curve and Chi square test, and the longitudinal analysis using multivariate Cox-regression.

Results: Eighty-four bipolar disorder patients were included in the analyses. Cross-sectionally, no statistically significant difference was found in CRP distribution across mood states (p = 0.372) or rapid cycling state (p = 0.656). Also, no CRP cut-off level was distinguished between euthymic and non-euthymic patients according to the ROC curve (p = 0.449, AUC = 0.452, 95 % CI 0.327, 0.576), and a literature-derived cut-off value (3 mg/L) again demonstrated no difference (p = 0.530). Longitudinally, no association was found between CRP and prognosis of disease neither in euthymic [-2 log likelihood = 120.460; CRP: p = 0.866, B = -0.011, OR = 0.989 (95 % CI 0.874-1.120)] nor non-euthymic patients [(-2 log likelihood = 275.028; CRP: p = 0.802, B = 0.010, OR = 1.010 (95 % CI 0.937-1.088)]. Medication use did not affect these associations.

Conclusions: We found no statistically significant association between CRP and a more unfavorable BD prognosis, suggesting that the application of CRP as a practical biomarker to predict outcome in a naturalistic outpatient care setting is not as straightforward as it may seem.