Spectrum of hematological changes in COVID-19.

Coronavirus disease 2019 (COVID-19) is caused by pathogenic and highly transmissible Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) which is a single stranded RNA virus. It rapidly emerged from an epidemic to a global pandemic form spreading in alarming levels. The pathogenesis involving spike protein which is present on the viral surface, plays a key role in host attachment and penetration. SARS-CoV-2 infection significantly affects respiratory system, but may involve other systems including haematopoietic system and homeostasis. Aim of the review article is to discuss spectrum of haematological changes in the blood counts, coagulation, peripheral blood and bone marrow in COVID-19 for complete understanding the disease process, the knowledge of which is helpful in early diagnosis and management of these patients. An extensive immune profiling of B and T cell population with analysis of spectrum of immune changes during the period of infection were also discussed. In COVID-19, changes in laboratory parameters and hematologic abnormalities have been reported and its association with early diagnosis, disease prognosis and severity has been repeatedly discussed in the literature. Changes in laboratory investigations help in risk stratification and early intervention. The most common laboratory finding in COVID-19 is lymphopenia. COVID-19 patients presented with coagulopathy is at high risk of morbidity and mortality. In severe COVID-19 patients, bone marrow aspirate shows histiocytic proliferation with hemophagocytosis. To understand the correlations between immune responses and severity of COVID-19, immune profiling of B and T cell population was compared with extensive clinical data. A deep understanding of the laboratory findings and haematological abnormalities associated with SARS-CoV-2 infection would help to raise disease suspicion in absence of Real time polymerase chain reaction or antibody results. Also the blood counts along with the morphological changes in peripheral blood would be helpful in prompt screening, diagnosis, prognosis and management of COVID-19 patients.