Systematic Evaluation of Hematological Parameters and Blood Smear Findings Reveals Significantly Fewer Abnormalities in Patients Admitted with SARS-CoV-2 Compared to Other Viral Respiratory Infections

Peripheral blood abnormalities like variant lymphocytes, Pelger-Huët anomaly, and granulocytic left shift have been reported in patients with active severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. However, the specificity of these findings for SARS-CoV-2 infection is unknown as there is a lack of comparative data between SARS-CoV-2 and other viral respiratory illnesses. In this study, we examined the peripheral blood findings in patients admitted with acute SARS-CoV-2 and other viral respiratory infections. We reviewed the complete blood differential counts and peripheral blood leukocyte morphology on peripheral smears received from patients admitted with a positive viral respiratory panel (VRP) or SARS-CoV-2 test from March 20th – May 31st, 2020. Cases where the specimen was collected 10 days after the symptom onset were excluded. During the study period, we reviewed 122 blood specimens from 59 patients (mean±SD age: 46.7±21.7 years, female: 49.2%). Of these, 53 (43.4%) specimens were from patients with SARS-CoV-2 infection and 69 (56.6%) specimens from patients with other viral respiratory infections. There were no significant differences in the demographic characteristics of the two groups. For the blood cell counts, absolute leukopenia (11.3% versus 40.6%, P<0.001), low red blood cell count (45.3% versus 78.3%, P<0.001), low hemoglobin (56.6% versus 76.8%, P0.018), low hematocrit (43.4% versus 78.3%, P<0.001), high mean corpuscular volume (3.8% versus 31.9%, P<0.001), high mean corpuscular hemoglobin concentration (1.9% versus 14.5%, P0.016), thrombocytopenia (11.3% versus 58.0%, P<0.001), low mean platelet volume (3.9% versus 15.0%, P0.048), and high red cell distribution width (13.2% versus 53.6%, P<0.001) were all less common in patients with SARS-CoV-2 infection as compared to those with other viral respiratory infections. There were no significant differences in the differential leukocyte counts between the two groups, except neutropenia was less common in SARS-CoV-2 infection (17.3% versus 44.1%, P0.002). Among the peripheral blood smear findings, toxic granulation in neutrophils (1.9% versus 42.01%, P<0.001) and the presence of myelocytes (13.2% versus 29.0%, P0.042) were less commonly seen in SARS-CoV-2 infection. Other findings like elevated band neutrophils (8.3% versus 27.5%, P0.081), presence of metamyelocytes (13.2% versus 27.5%, P0.060), presence of promyelocytes (5.7% versus 13.0%, P0.186), plasmacytoid lymphocytes (66.7% versus 91.7%, P0.177), and hypogranular neutrophils (7.6% versus 8.7%, P0.819) showed a trend towards being less common in patients with SARS-CoV-2 infection but the differences were not statistically significant. On the contrary, reactive lymphocytes (43.4% versus 33.3%, P0.257) and uni- or bi-lobate neutrophils showed a trend towards being more common in SARS-CoV-2 infection (18.9% versus 17.4%, P0.833), however, the differences were not statistically significant. Abnormalities in peripheral blood count and blood smear findings seem to be less frequent in hospitalized patients with SARS-CoV-2 infection as compared to those with other viral respiratory infections.