BDNF and depressive symptom measurement: In the retrospective study by Yang et al. (2010), which prospectively investigated whether serum BDNF is associated with the development of depression in the acute phase, it was found that the mean serum BDNF level in PSD patients was significantly lower than in non-PSD patients as early as 1 day after stroke and that the serum BDNF level < 5.86 ng/mL at day 1 was independently associated with the occurrence of PSD in the acute phase of stroke (OR.28.99; 95% CI, 8.014–104.891; p < 0.001 after adjustment) [42].