Abstract: Due to the reproductive characteristics of Plasmodium parasites, special inclusion bodies are formed in the red blood cells infected with Plasmodium parasites, which can be identified by microscopic examination. Microscopic examination of blood smears has become the most commonly used method for laboratory diagnosis of malaria. However, in the absence of information such as the patient's medical history, diagnosis or corresponding examination orders, laboratory doctors lack sensitivity to Plasmodium parasite infections. This study reports two cases of Plasmodium parasite-infected patients whose red blood cells infected with Plasmodium parasites in peripheral blood led to abnormal blood routine test results. One of the patients showed a pseudo-increase in eosinophils, and the position of eosinophils in the white blood cell scatter plot was abnormal. The other patient showed a pseudo-increase in reticulocyte count, and the reticulocyte scatter plot presented a "starry sky" shape. It was confirmed by microscopic examination of peripheral blood smears and analyzed in combination with the patient's medical history, microscopic counting, and the principle of instrument detection. It was determined that different developmental stages of Plasmodium parasites in red blood cells could lead to different lateral scattered light and lateral fluorescence intensities detected by the instrument and be misjudged as different cells. This analysis can provide a reference for laboratories and clinicians to warn or identify Plasmodium parasite infections through blood routine scatter plots.

Key words: Plasmodium, Eosinophil, Reticulocytes, Scatter diagram, Routine blood test