Objective:To investigate the level and changing trend of microparticles (MPs) in super-elderly infected patients, and explore its early warning effect on infection.Methods:The infected patients ≥ 85 years old admitted to the Second Medical Center of Chinese PLA General Hospital from December 2018 to March 2019 were selected as the observation group, and the healthy volunteers ≥ 85 years old in the same period were selected as the control group. Venous blood samples were collected at the 2nd hour, the 2nd day and the 7th day after fever, and the inflammatory markers such as white blood cell count (WBC), neutrophil percentage (NEUT), C-reactive protein (CRP) and procalcitonin (PCT) were measured. The levels of MPs were determined by flow cytometry. AnnexinⅤlabeled CD11b positive MPs (AnnexinⅤ +/CD11b + MPs) represented leukocyte microparticles (LMPs), and AnnexinⅤlabeled CD66b positive MPs (AnnexinⅤ +/CD66b + MPs) represented neutrophil microparticle (NMPs). The differences of each index at different time points between the two groups were compared, and the predictive value of each index to the infection of elderly patients was analyzed by receiver operating characteristic (ROC) curve. Results:A total of 38 subjects were enrolled, including 28 cases in the observation group and 10 cases in the control group. The levels of LMPs and NMPs in the observation group increased to the peak at the 2nd hour after fever, and were significantly higher than those in the control group [LMPs (cells/μL): 55.0 (28.8, 197.2) vs. 19.0 (13.5, 28.3), NMPs (cells/μL): 226.5 (123.3, 516.5) vs. 26.5 (22.0, 48.8), both P < 0.01]. With the control of the disease, LMPs and NMPs decreased gradually. The NMPs on the 2nd day was significantly lower than that at the 2nd hour of fever [cells/μL: 106.0 (40.0, 309.0) vs. 226.5 (123.3, 516.5), P < 0.05], and the LMPs and NMPs on the 7th day were significantly lower than those on the 2nd day [LMPs (cells/μL): 17.0 (12.5, 43.8) vs. 42.0 (13.0, 117.0), NMPs (cells/μL): 30.0 (15.8, 62.0) vs. 106.0 (40.0, 309.0), both P < 0.05]. There was no significant difference in the levels of LMPs and NMPs between the two groups on the 7th day. Among the inflammatory markers, the NEUT in the observation group was significantly higher than that in the control group at the 2nd hour of fever (0.70±0.09 vs. 0.59±0.04, P < 0.01), but there was no significant difference in WBC, CRP and PCT between the two groups. On the 2nd day, the inflammatory markers in the observation group reached the peak and were significantly higher than those in the control group [WBC (×10 9/L): 9.33±2.44 vs. 6.37±1.28, NEUT: 0.78±0.08 vs. 0.57±0.04, CRP (mg/L): 5.67±2.99 vs. 0.33±0.18, PCT (μg/L): 0.80±0.67 vs. 0.07±0.03, all P < 0.01]. On the 7th day, the inflammatory markers in the observation group decreased significantly, and there was no significant difference between the observation group and the control group. ROC curve analysis showed that the area under ROC curve (AUC) and 95% confidence interval (95% CI) of LMPs and NMPs on the day of fever were higher than those of WBC, NEUT, CRP and PCT [0.888 (0.763-1.000), 0.973 (0.931-1.000) vs. 0.679 (0.346-0.811), 0.829 (0.700-0.958), 0.607 (0.404-0.811), 0.554 (0.358-0.749)]. Conclusion:LMPs and NMPs are significantly increased in the early stage of fever, which can predict the incidence of infection in the super-elderly patients.