CHI3L1 and Alzheimer disease: The subgroup based on blood component samples (serum/plasma) analysis showed that the YKL-40 significantly differed between AD patients and healthy controls in plasma (SMD = 0.527, 95%CI: [0.302, 0.752]; p = 0.000), but not in the serum (SMD = −0.638, 95%CI: [−2.636, 1.361]; p = 0.532; Table 2, Figure S1).