Background: Reverse Transcriptase-Polymerase Chain Reaction (RT-PCR) SARS-CoV-2 assay remains the common test used to detect the coronavirus infection worldwide. Complete blood count (CBC) is a rapid and cost-effective test compared to RT-PCR, thus, it would be worthy to find a hematological indicator for SARS-CoV-2 infection. Objectives: This study aims to assess the efficacy of CBC indices as an initial diagnostic test for coronavirus 2019 (COVID-19) infection, which might be helpful during the outbreak of the disease. Materials and Methods: A retrospective, hospital based and case control study was carried out at Gezira isolation center for COVID-19, Gezira State, Sudan in the period from January to May 2021. A total of 178 COVID-19 patients with positive RT-PCR SARS-CoV-2 assay result and another 178 volunteers of apparently healthy people were included in this study. CBC as well as D-dimer and C-reactive protein (CRP) were recorded from patient’s file and neutrophil-to-lymphocyte ratio (NLR), platelet-to-lymphocyte ratio (PLR) and lymphocyte-to-monocyte ratio (LMR) were calculated. Data were analyzed using Statistical Package for Social Science (SPSS) version 20. Results: Neutrophil percentage, total white blood cells (TWBCs) and platelet (PLT) were higher in the COVID-19 patients compared to their control, whereas, lymphocyte and monocyte showed lower percentages among the COVID-19 patients. Although the differences that observed in the means of PLT, neutrophils and monocytes between the case and control group were significant, all these mean values of both groups were lying within the normal range. On the other hand, there was a highly significant elevation in NLR and PLR and quite good increasing in LMR level among COVID-19 patients compared to their control. The results of receiver operating characteristic curve (ROC) analysis showed that the area under the curve of NLR, PLR and LMR were 0.948 (P. value = 0.00, 95% CI: 0.925 - 0.972), 0.925 (P. value = 0.00, 95% CI: 0.896 - 0.954) and 0.643 (P. value = 0.00, 95% CI: 0.584 - 0.702), respectively, suggesting the efficacy of using these tests as diagnostic tests for COVID-19 infection. D-dimer and CRP level were highly elevated in COVID-19 patients with significant differences compared to control group. Recommendation: The study recommends using NLR, PLR and LMR as rapid initial diagnostic test for SARS-CoV-2 infection in the area/time of disease spread out.