Abstract: Background of the Study: Bacterial and Viral infections are often hard to be distinguished in daily clinical practice. Biological markers obtained from a routine examination play an important role to minimize time in providing diagnose and giving therapy. Recently, the use of Neutrophil-lymphocyte ratio (NLR), monocyte-lymphocyte ratio (MLR), and platelet-lymphocyte ratio (PLR) is greatly considered to differentiate types of infection found in the patients presenting with fever. Method: This study uses prospective cohort study design and involves patients presenting with fever who are admitted to the ICU. The initial NLR, MLR, and PLR is examined and categorized into types of infection found. The ANOVA test and t-test are performed to find out the difference among study groups with the value of α = 0,05. Result : This study involves 207 patients (92 male patients [44%]) presenting with fever with the average age of 45,6 ± 14,6 years old. The majority of cases (135 cases [66,5%]) in patients with fever results from bacterial infection; The study also finds 47 cases (34,8%) of typhoid fever and 30 cases (22,2%) of pulmonary tuberculosis. Dengue hemorrhagic fever (DHF) is the most commonly found viral infection with 52 cases (76,4%). The significant diagnose of bacterial infection shows higher value of NLR and MLR than that of viral infection (P < 0,001); Urinary tract infection has the highest value of NLR and MLR, amounting to 9,4 ± 3,6 and 0,23 ± 0,20, respectively. In general, the value of PLR is lower than that of viral infection (P < 0,001). Conclusion: Neutrophil-lymphocyte ratio, MLR and PLR have benefit to predict diagnosis for the patients presenting with a fever. Bacterial infection is associated with the high value of NLR and MLR, and PLR generally has a lower value in viral infection cases.