Aim: In this study, the roles of biomarkers from a peripheral blood sample in the diagnosis of COVID-19 patients who have visited the emergency room have been evaluated. Materials & methods: Peripheral blood parameters, systemic inflammatory index (SII), neutrophil lymphocyte ratio (NLR) and platelet lymphocyte ratio were compared in patients with and without confirmed COVID-19 infection. Results: Comparisons made according to real-time PCR test results revealed that while no statistically significant difference was observed between test groups (negative-positive) regarding lymphocyte and platelet lymphocyte ratio values (p > 0.05), a statistically significant difference (p < 0.05) was found between the test groups regarding platelet, hemoglobin, leukocyte, neutrophil, NLR and SII values. Conclusion: Leukocyte, neutrophil, platelet count, NLR and SII values can be used in the diagnosis of COVID-19.