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Coronavirus disease 2019 (COVID-19): Focus on peripheral blood cell morphology
Gina Zini1,2, Giuseppe d'Onofrio1
1Haematology, Catholic University of Sacred Heart, Rome, Italy.
Insights
COVID-19 infections cause unique changes in blood cell appearance. These include alterations in lymphocytes, neutrophils, monocytes, and platelets, reflecting severe systemic inflammation.
Area of Science:
- Hematology
- Infectious Diseases
- Cellular Morphology
Background:
- COVID-19 is associated with various clinical manifestations.
- Peripheral blood smear analysis is a routine diagnostic tool.
- Morphological anomalies in blood cells of COVID-19 patients have been reported.
Purpose of the Study:
- To systematically review and synthesize findings on cytomorphological alterations in peripheral blood smears of COVID-19 patients.
- To identify common and distinctive blood cell changes associated with COVID-19.
Main Methods:
- Comprehensive literature search of peer-reviewed publications on COVID-19 and peripheral blood smear morphology.
- Data extraction from sixty-five selected studies, including case reports, patient group studies, reviews, and erythrocyte morphology studies.
Main Results:
- Frequent alterations observed in lymphocytes (e.g., plasmacytoid, large granular).
- Distinctive neutrophil changes noted, including hyposegmentation (pseudo-Pelger-Huët anomaly) and altered granulation.
- Monocyte and platelet morphology abnormalities (vacuolation, giant forms) and erythrocyte fragments/schistocytes in thrombotic microangiopathy cases were evident.
Conclusions:
- Observed blood cell atypia in COVID-19 reflects generalized systemic activation, particularly in severe cases.
- Neutrophilpathophysiology is implicated in the hyperinflammation and cytokine storm characteristic of severe COVID-19.
- Peripheral blood smear analysis can provide valuable insights into COVID-19 pathophysiology and severity.
Abstract:
Numerous studies have shown peculiar morphological anomalies in COVID-19 patients' smears. We searched all the peer-reviewed scientific publications that explicitly reference the cytomorphological alterations on peripheral blood smears of patients with COVID-19. We extracted data from sixty-five publications (case reports, patient group studies, reviews, and erythrocyte morphology studies). The results show that frequent alterations concern the morphology of lymphocytes (large lymphocytes with weakly basophilic cytoplasm, plasmacytoid lymphocytes, large granular lymphocytes). Neutrophils display abnormal nuclei and cytoplasm in a distinctive cytomorphological picture. Besides a left shift in maturation, granulations can be increased (toxic type) or decreased with areas of basophilia. Nuclei are often hyposegmented (pseudo-Pelger-Huёt anomaly). Apoptotic or pycnotic cells are not uncommon. Monocytes typically have a large cytoplasm loaded with heterogeneous and coalescing vacuoles. Platelets show large and giant shapes. The presence of erythrocyte fragments and schistocytes is especially evident in the forms of COVID-19 that are associated with thrombotic microangiopathies. Such atypia of blood cells reflects the generalized activation in severe COVID-19, which has been demonstrated with immunophenotypic, molecular, genetic, and functional methods. Neutrophils, in particular, are involved in the pathophysiology of hyperinflammation with cytokine storm, which characterizes the most unfavorable evolution.
