A subset (n = 29) of the present TRD sample (n = 40) was previously included in a study (Kruse et al., 2018) that examined whether changes in inflammation occur over the course of ECT (T1, T2 and T3) and whether changes in IL-6 or CRP (from T1 to T2) predicted global improvement in depression severity. Here, CRP is linked to major depressive disorder.