Peripheral Blood Examination Findings in SARS-CoV-2 Infection

Alia Nazarullah, MD; Christine Liang, MD; Andrew Villarreal, MLS; Russell A. Higgins, MD; Daniel D. Mais, MD


Am J Clin Pathol. 2020;154(3):319-329. 

In This Article

Abstract and Introduction


Objectives: Peripheral blood abnormalities in severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) have not been fully elucidated. We report qualitative and quantitative peripheral blood findings in coronavirus disease 2019 (COVID-19) patients and compare them with a control group.

Methods: We reviewed electronic medical records, complete blood counts, peripheral blood smears, and flow cytometry data in 12 patients with SARS-CoV-2. These were compared with 10 control patients with symptoms suspicious for SARS-CoV-2 but who tested negative.

Results: No significant differences were noted in blood counts, except that absolute lymphopenia was present frequently in the control group (P < .05). Acquired Pelger-Huët anomaly (APHA) was noted in all COVID-19 cases, in most cases affecting over 5% of granulocytes. This contrasted with APHA in only 50% of control cases, affecting fewer than 5% of granulocytes in all cases (P < .05). Monolobate neutrophils were exclusive to COVID-19 cases. COVID-19 patients had greater frequency of plasmacytoid lymphocytes (P < .05). Flow cytometry data revealed absolute CD3+ T-cell count reduction in 6 of 7 patients; all of them required mechanical ventilation.

Conclusions: Lymphopenia was infrequent in our COVID-19 cohort; however, flow cytometric analysis revealed absolute T-cell count reduction in most cases. COVID-19 cases had significant APHA with monolobate neutrophils and plasmacytoid lymphocytes as compared to controls.


Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the causative agent of the coronavirus disease 2019 (COVID-19) pandemic, is a highly contagious enveloped single-stranded RNA virus that belongs to the family of Betacoronaviruses.[1] This virus shares genomic and clinical similarities with the other highly pathogenic coronaviruses, namely severe acute respiratory syndrome coronavirus (SARS-CoV) and Middle East respiratory syndrome coronavirus (MERS-CoV), which caused fatal epidemics in 2002 and 2012 respectively.[2] SARS-CoV-2 infections can range from asymptomatic carriers to mild respiratory symptoms and fatal acute respiratory distress syndrome. The virus is thought to cause T-cell immune dysregulation, especially in immunocompromised patients, resulting in monocyte/macrophage activation, uncontrolled cytokine release, and fatal multiorgan dysfunction.[3] Laboratory findings reported in association with COVID-19 include leukopenia, lymphopenia, monocytosis, neutrophilia, eosinopenia, and thrombocytopenia.[4–6] To the best of our knowledge, peripheral blood smear morphologic findings are reported in detail in less than 5 publications to date in the literature.[7–10] The reported abnormalities in peripheral blood smear include a range of reactive lymphocytes, abnormal platelet morphology, leukoerythroblastosis, and one publication on acquired Pelger-Huët anomaly (APHA). In this study, we report peripheral blood abnormalities, with emphasis on peripheral blood smear morphology, in 12 cases of SARS-CoV-2 infection and compare them with a control group.