The subgroup analysis according to the AD criteria revealed that YKL-40 levels were significantly higher in AD patients diagnosed by using NIA-AA than in HCs (SMD = 0.498, 95%CI: [0.281, 0.715]; p = 0.000; I2 = 0.0%, p = 0.637), but high heterogeneity remained between studies in NR group (SMD = −1.009, 95%CI: [−3.917, 1.899]; p = 0.497; I2 = 97.4%, p = 0.000; Table 2, Figure S3). This evidence concerns the gene CHI3L1 and Alzheimer disease.