Serum brain-derived neurotrophic factor in bipolar and unipolar depression: a potential adjunctive tool for differential diagnosis

The differential diagnosis of Bipolar Disorder (BD) and Major Depressive Disorder (MDD) is a diagnostic challenge during depressive episodes. Noteworthy, the proper differentiation between BD depressive state and MDD has important treatment implications. BDNF levels may be valuable adjunctive tool for this differential diagnosis. Ten subjects with MDD, forty with BD type I and thirty healthy comparison subjects were recruited. All subjects had BDNF serum levels measured and, in patients, BDNF serum levels were assessed during acute depressive episode. Optimal sensitivity and specificity of serum BDNF for the differential diagnosis of unipolar and bipolar depression were determined by the receiver operating characteristic (ROC) curve analysis, using a nonparametric approach. Serum BDNF levels in depressive BD patients were lower compared to MDD patients and controls (0.15 ± 0.08, 0.35 ± 0.08, and 0.38 ± 0.12, respectively, p < 0.001). The area under the curve (AUC) of the ROC analysis in BD depression vs. MDD was 0.95 (ranged from 0.89 to 1.00). Overall, the AUC of the ROC analysis (BD depression vs. MDD and controls) was 0.94 (95% CI 0.89 to 0.99, p < 0.001). A proposed “best” cutoff of 0.26 resulted in 88% sensitivity and 90% specificity. Serum BDNF levels appear as a promising tool to discriminate bipolar from unipolar depression. Our results suggest the role of BDNF as an adjunctive tool to promote prompt and accurate diagnosis of BD. However, further investigation and replication of these results are warranted.