C-Reactive Protein as an Indicator for Antidepressant Response in Late-Onset Depression: A prospective Study

Introduction: Late-onset depression (LOD), often linked to immune dysfunction and vascular factors, presents distinct treatment challenges compared to early-onset depression. Predicting treatment outcomes remains difficult. We hypothesized that baseline levels of C-reactive protein (CRP), an inflammatory marker, may correlate with antidepressant response in individuals experiencing their first episode of LOD. Methods: This prospective study recruited subjects aged >60 years presenting with their first depressive episode (ICD-10 DCR criteria). Baseline assessments included clinical evaluation, serum CRP measurement (mg/L), and depression severity using the 17-item Hamilton Depression Rating Scale (HAMD-17). Participants received standard antidepressant treatment (Escitalopram) for 8 weeks, after which HAMD-17 was reassessed. Treatment response was defined as ≥50% reduction in HAMD-17 score from baseline. Results: Of 64 eligible participants, twenty-five participants (mean age 64.7±5.8 years; baseline HAMD-17 score 18±3) completed the 8-week follow-up. The overall antidepressant response rate was 24% (n=6 responders). Responders (n=6) had a mean baseline HAMD-17 score of 16±1.9, while non-responders (n=19) had a mean baseline score of 18.6±3.1. The mean baseline CRP level was significantly higher in non-responders (6.27 ± 1.58 mg/L) compared to responders (3.80 ± 1.40 mg/L) (p = 0.002). A significant negative correlation was observed between baseline CRP levels and antidepressant response (r = –0.588, p = 0.02). Conclusions: In this preliminary study of older adults with first-episode LOD, elevated baseline CRP levels were associated with a poorer response to an 8-week course of standard antidepressant therapy suggesting that systemic inflammation may be a potential predictive biomarker for treatment outcomes in this population. Keywords C-reactive protein, Late onset depression, Antidepressant