Evaluation of the diagnostic accuracy of combined detection of serum homocysteine (Hcy), C-reactive protein (CRP), and serum ferritin (SF) levels in patients with Alzheimer's disease (AD) and mild cognitive impairment (MCI).Descriptive study. Place and Duration of the Study: Clinical Laboratory Section, Affiliated Hospital of Hebei University, Baoding, Heibei, China, from May 2022 to June 2023.Data of 120 patients with memory decline were retrospectively collected. They were divided into an MCI group and an AD group. A further 50 healthy participants were used as a normal control (NC) group. Differences in the Hcy, CRP, and SF levels between the three groups were evaluated. The specificity, accuracy, and sensitivity of these three indices in the combined or single diagnosis of AD and MCI were compared. Their associations with the severity of AD and MCI were also compared.The AD group had the highest levels of Hcy, CRP, and SF (18.79 ± 4.50, 6.35 ± 2.04, and 355.69 ± 120.36), followed by MCI (16.75 ± 3.06, 4.58 ± 2.31, and 203.48 ± 12.76), and NC group (14.32 ± 2.06, 2.06 ± 0.76, and 98.46 ± 5.06), with statistically significant differences (all p <0.001). The diagnostic efficacy of AD for CRP was 98.50%, sensitivity was 96.00%, and specificity was 94.00%, which was higher than Hcy and SF. Tested together, the area under the ROC curve was 99.90%, specificity was 98.00%, and sensitivity was 98.00%. The diagnostic efficacy of SF for MCI had sensitivity of 100.00%, and specificity of 100.00%, which was higher than that of Hcy and CRP. When the three were combined for detection, the area under the curve of SF was 100.00%, sensitivity of 100.00%, and specificity of 100.00%. The levels of Hcy, CRP, and SF were positively correlated with the severity of AD (p <0.01), while negatively correlated with the mini-mental state examination (MMSE) score (p <0.01).The combined detection of Hcy, CRP, and SF improved the diagnostic accuracy of comorbid AD and MCI.Homocysteine, C-reactive protein, Cognitive impairment, Serum ferritin, Alzheimer's disease.