In the last decades, coronaviruses have been a major threat to public health worldwide. SARS-CoV-2 is the third known coronavirus that causes fatal respiratory diseases in humans. The initial clinical features of SARS-CoV-2 infection are quite nonspecific and not all suspected patients can be tested to exclude or confirm the diagnosis. Increasing scientific evidence has shown that abnormalities in routine laboratory tests, particularly hematological tests, have the potential to indicate, in a quick, practical and economical way, the need for specific laboratory tests for the diagnosis of SARS-CoV-2 infection, besides assisting in the prognosis of the disease and in the optimization of its clinical monitoring. In order to address in a simple and practical way the various aspects related to SARS-CoV-2 infection, this review reports the history of the virus, the epidemiology and pathophysiology of COVID-19, with emphasis on its laboratory diagnosis, particularly in hematological changes found during the course of the disease.