APOE and Alzheimer disease: The combined sensitivity was 0.62 (95% CI (0.58, 0.66)), specificity was 0.84 (95% CI (0.81, 0.86)), positive likelihood ratio was 3.8 (95% CI (3.3, 4.3)), negative likelihood ratio was 0.45 (95% CI (0.41, 0.49)), area under ROC curve was 0.80, and diagnostic ratio (DOR) was 8, which indicated the APOE ε4 has a medium value in the diagnosis of AD.