IL6 and concussion: Further sub-analysis based on timing, i.e., acute and chronic stages showed significantly elevated circulating IL-6 levels in mTBI population compared to healthy population in the acute stages (less than 7 days) (SMD: 0.49 [0.21, 0.77] pg/mL, p = 0.0007, I2 = 55%) (Figure 3B).