BDNF and chronic kidney disease: The pooled effect size demonstrated a statistically significant reduction in serum BDNF levels among CKD patients (WMD = −0.62 ng/mL, 95% CI [−0.98, −0.25], P < 0.001), accompanied by substantial heterogeneity across studies (I2 = 87%, P < 0.001) (Figure 2).