Evaluation of sensitivity and specificity of high fluorescence lymphocyte count percentage of sysmex XN analyzer in diagnosis of dengue

BACKGROUND: The Sysmex XN-series hematology analyzers provide newer parameters including high fluorescence lymphocyte cell percentage (HFLC%) which correlates with the presence of atypical lymphocytes in peripheral blood. We aimed to analyze the sensitivity and specificity of HFLC% as a diagnostic tool and its association with serological status in diagnosed dengue patients and thereby establish a cutoff of HFLC% based on serology. Besides, we also wish to correlate HFLC% with thrombocytopenia in these patients. MATERIALS AND METHODS: A total of 1500 serum samples were subjected to serological evaluation for dengue. After excluding hematological malignancies and autoimmune disorders, the same day complete blood count parameters including HFLC% and platelet counts were collected retrospectively for 292 serologically positive dengue cases and 76 seronegative controls. RESULTS: Our result shows that in nonstructural 1 antigen-positive cases, a cutoff of >5.2% HFLC can have a sensitivity of 79.5% and specificity of 98.6%. We found a different cut off of HFLC% >3.2% (sensitivity 83.4%, specificity 98.6%) for the cases with only immunoglobulin M positivity and a cut off of HFLC% >2.6% (sensitivity 86.1%, specificity 96%) in the dual positive cases (immunoglobulin M with nonstructural 1 antigen). Besides, high HFLC% also shows a strong correlation with platelet count with a Spearman correlation coefficient of −0.6. CONCLUSIONS: The result of our study shows that a specific cutoff of HFLC% can not only help us to suspect dengue fever but also predict the risk of thrombocytopenia in already diagnosed dengue patients. The sensitivity and specificity of HFLC% varied with the serological status of the patients which depend on the days of fever on presentation.