When diagnostic criteria were used as the basis for subgroup analysis, we found that CSF levels of YKL-40 were significantly higher in AD patients than HCs in both studies with NINCDS-ADRDA (SMD = 0.763, 95%CI: [0.530, 0.996]; p = 0.000; Table 3, Figure S5) and DSM-III-R (SMD = 0.487, 95%CI: [0.205, 0.769]; p = 0.001; Table 3, Figure S5) as the diagnostic criteria, and heterogeneity between studies in both the NINCDS-ADRDA (I2 = 0.4%, p = 0.390; Table 3, Figure S5) criteria group and the DSM-III-R (I2 = 0.0%, p = 0.741; Table 3, Figure S5) criteria group did not exist. Here, CHI3L1 is linked to Alzheimer disease.