OBJECTIVE To analyze the characteristics of peripheral blood leukocyte morphology, scatterplot and leukocyte cell population data (CPD) in patients with severe fever and thrombocytopenia syndrome (SFTS), infectious mononucleosis (IM) and hemorrhagic fever with renal syndrome (HFRS), and to explore their differences.

METHODS Blood routine examination data were collected, including microscopic cell images, scatterplots and leukocyte CPD study parameters from 44 patients diagnosed with SFTS, 17 with IM and 11 with HFRS at the First Affiliated Hospital with Nanjing Medical University from Mar. 2023 to May 2024. These data were compared with those of healthy controls to explore specific differences in the characteristics of peripheral blood leukocyte.

RESULTS All 3 viral infections exhibited a left shift in the nucleus under the microscope, yet the blood routine scatterplot and microscopic leukocyte characteristics differed. SFTS commonly presented with a plasmacytoid reactive lymphocyte with scattered points appearing in the upper reactive lymphocyte area of the scatterplot. IM showed a predominant irregular fried-egg-like reactive lymphocyte under the microscope, with the scatterplot typically presenting a rocket-like shape, in patients with HFRS, there was a significant increase in immature granulocytes in peripheral blood and plasmacytoid reactive lymphocyte scatter points with blue immature granulocyte scatter points visible. The fluorescence distribution width (MO-WY) of monocytes in the SFTS group was lower than those in the IM, HFRS and healthy control groups (P < 0.05). Compared to SFTS, IM and healthy control groups, the lateral scattered light distribution width (NE-WX) and fluorescence distribution width (NE-WY) of neutrophils in the HFRS group were both increased (P < 0.05).

CONCLUSIONS There are significant differences in the characteristics of peripheral blood leukocyte morphology, scatterplot and CPD study parameters among three viral infection diseases SFTS, IM and HFRS. These differences can provide early clinical advice and assist in clinical differentiation.