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Affective disorders affect approximately 12% of the global population and include major depressive disorder (MDD) and bipolar disorder (BD), which often present with clinically indistinguishable depressive episodes. This highlights the need to identify reliable biomarkers for diagnostic differentiation. In this study, serum platelet-derived growth factor BB (PDGF-BB) and plasma thrombospondin-1 (TSP-1) were quantified by ELISA in 63 patients with MDD, 43 patients with BD, and 61 healthy controls. Patients were assessed during an acute depressive episode (T1) and in a (partially) remitted state (T2). Depressive symptom severity was evaluated using the Montgomery-Åsberg Depression Rating Scale (MADRS) (at T1: MDD = 33.16 ± 8.1; BD = 28.16 ± 9.74). Group differences and longitudinal changes were analyzed using non-parametric statistics, with adjustment for age, body mass index, and medication. PDGF-BB levels differed significantly between diagnostic groups during acute depression. Longitudinal analyses revealed significant lower levels of PDGF-BB from T1 to T2 in BD patients, but not in MDD patients, indicating a state-dependent change associated with remission in BD. These effects remained significant after adjustment for potential confounders, including lithium treatment. In contrast, TSP-1 levels showed no group- or state-dependent differences. When replicated, PDGF-BB may serve as a diagnostic biomarker distinguishing MDD from BD during acute episodes and as a potential state marker reflecting remission in bipolar disorder, even after accounting for relevant clinical confounders. • PDGF-BB differentiates major depression disorder from bipolar disorder during acute depressive episodes • Major depression is associated with lower serum PDGF-BB levels • PDGF-BB levels decrease with remission in bipolar but not major depression • Diagnostic and state-dependent effects remain significant after adjusting for confounders • Thrombospondin-1 shows no diagnostic or state-related differences
Cardona et al. (2026) studied this question.