CHI3L1 and early-onset autosomal dominant Alzheimer disease: However, CSF YKL-40 levels showed no statistically significant difference between AD and MCI groups (SMD = 0.25, 95%CI: [-0.08, 0.57]; <i>p</i> = 0.134).<h4>Discussion</h4>Elevated YKL-40 levels in both CSF and peripheral blood are associated with the presence of Alzheimer's disease and its early stages, indicating that YKL-40 reflects neuroinflammatory processes involved in AD onset.