Objective: Dengue infection (DI) is the most common arthropod-borne viral disease with symptoms ranging from mild flu like illness to fatal hemorrhagic fever. Thrombocytopenia is one of the common manifestations of dengue which can lead to life threatening bleeding. Currently, there is no validated test available that can predict the severity of thrombocytopenia in a dengue patient. Dengue has been well associated with presence of high fluorescence lymphocytes in the peripheral blood. High fluorescence lymphocyte count (HFLC) is a parameter generated at no extra cost when an automated complete blood count (CBC) is performed on Sysmex XN-1000 automated hematology analyzer. We aim to assess the significance and correlation of the HFLC with thrombocytopenia during the course of dengue infection especially during day 1 to 5 of the infection. Material and Methods: This is a cross sectional study and was conducted at Chughtai Institute of Pathology from August 2021 to October 2021. Total 312 patients, both males and females, who had NS1 positive confirmed dengue infection were included in the study. Their platelet count and HFLC were noted at the time of diagnosis using Sysmex XN-1000. Follow up CBC were analyzed for next 5 days to observe the severity of thrombocytopenia. Results: There is significant negative correlation between absolute HFLC and platelet count on day one to five of the infection. On receiver operator characteristic curve analysis, we found that HFLC < 0.5 x103/µL had 60% sensitivity and 71.8% specificity for severe thrombocytopenia (platelet count less than 50 x 103/µL on day 5 of the infection. Conclusion: HFLC is a negative predictive factor for severe thrombocytopenia and therefore can be used as an early predictor of disease progression. Key Words: Dengue infection, NS1 antigen, High fluorescence lymphocyte count, Thrombocytopenia, Automated hematology analyzer.