Background: Dengue fever is the most common arbovirus infection in the world. Clinical manifestation range from fever to dengue shock syndrome (DSS). Clinical diagnosis can be difficult, as its presenting signs and symptoms can easily be confused with other febrile illnesses. Though specific diagnostic tests like NS1 antigen and dengue specific IgM antibody by immunochromatography are currently available for rapid diagnosis and early management in secondary and tertiary care centers, resource limited settings have problems with the early detection, due to non availability of such expensive diagnostic tests. Also, specific tests for monitoring the disease activity, has not come in to regular practice till date, in many parts of the world. Hence, in addition to early and accurate diagnosis, early markers of progression to severe disease are urgently needed. Aim of the study: To emphasize the importance of peripheral smear examination in the early assessment and monitoring of disease activity in patients with dengue fever. Methods: A prospective study of one year (January 2017 – December 2017), during which 132 patients with dengue fever (78 cases positive for NS1 antigen and 54 cases positive for anti Dengue IgM antibody), tested and confirmed by tests for NS1 antigen and Anti Dengue IgM antibody were selected for the study and their peripheral smears were simultaneously examined and the findings were noted and compared. The patients were followed up with serial platelet counts and band forms during their hospital stay. Results: The peripheral smear findings noted for all the 132 dengue positive patients were leucopenia (91%), neutropenia (89%), bandemia (80%), reactive lymphocytosis (95%) and thrombocytopenia (84%). There were 6 cases of dengue hemorrhagic syndrome and all such patients had very low platelet counts (<50000) and bandemia >15%. In all the cases, clinical improvement was consistently associated with rising platelet count along with clearance of band forms. Conclusion: These peripheral smear findings are consistently present in majority of the patients with dengue fever. Such findings can be considered for diagnosis and monitoring the disease activity of dengue fever, especially in resource limited settings for early diagnosis and effective management.

Keywords: Dengue; Bandemia; Thrombocytopenia; Reactive Lymphocytes; Leucopenia.