C-reactive protein as a biomarker for unipolar versus bipolar depression: a cross-sectional study

Background Differentiating unipolar depression from bipolar depression is clinically important. The identification of biomarkers that characterize the pathophysiology of each disorder may provide biological targets for treatment. The objective of the study was to demonstrate a relationship between CRP level and the severity of depressive symptoms and see if C-reactive protein (CRP) levels can be used as a biomarker to distinguish between unipolar and bipolar depression. A convenience sample of 90 individuals was consecutively recruited from the psychiatry outpatient clinic at Beni-Suef University Hospital, Egypt. They were divided into three equal groups: patients with major depressive disorder (MDD) (group 1), bipolar depression (group 2), and a healthy volunteer group (group 3). Patient groups were assessed using semi-structured interviews, and CRP levels were measured. Results Patients with bipolar depression and MDD showed a significantly higher score on the Beck Depression Inventory scale than the control group (32.97 +/- 2.4 vs. 31.93 +/- 2.3 vs. 8.00 +/- 2.3 in all groups respectively) (P-value < 0.001). Patients with bipolar depression and MDD showed a significantly higher serum CRP level than the control group (134.96 +/- 16.45 vs. 133.86 +/- 17.59 vs.56.04 +/- 26.71 vs. in all groups respectively) (P-value < 0.001). In all studied groups, elevated plasma CRP levels have a significant linear correlation with the severity of depression as measured by the Beck Depression Inventory (BDI) (r = 0.887, P-value < 0.001). Conclusions Serum CRP levels are significantly higher in MDD and BD patients when compared to controls. Individuals with higher CRP levels had more severe depression, and this finding was significantly higher in women than in men.