Discussion
In adults, the most common hematological findings of COVID-19 include
lymphocytopenia (11, 12), neutrophilia (2, 13), mild thrombocytopenia
(7) and, less frequently, thrombocytosis (9, 17). However, there is
paucity of data on hematological findings in affected children (4, 13).
In our study, the majority of the SARS-CoV-2 infected children had
normal leukocyte count, but 13.3% had leukopenia and 6.7% had
leukocytosis, according to age-specific intervals. Despite normal
leukocyte count, lymphopenia and neutrophilia were noted in 30.0% and
13.3% of children affected with the disease, respectively. Seven
patients with SARS-CoV-2 test positive (23.3%) had neutropenia; this
figure was 7.5% in the test negative group. Neutropenia has not been
previously reported in adults affected with the disease.
The presence of reactive lymphocytes has been occasionally reported in
adults with COVID-19. Fan et al. reported a few lymphoplasmacytoid
reactive lymphocytes in peripheral blood of lymphopenic patients with
COVID-19 (7). It is well documented in the literature that in response
to stress, atypical reactive lymphocytes that are characterized by
nuclear and cytoplasmic distortion appear in the blood (18). Reactive
lymphocytes were detected in 85.1% of our patients in the whole cohort,
77.8% in the test-positive and 90% in the test-negative groups. The
mean ARL count was lower in the COVID-19 positive group, which was
statistically different from the COVID-19 negative group.
Leukoerythroblastic reaction that reflects the immature erythroid and
immature myeloid cells circulating in the peripheral blood has also been
reported in adults with COVID-19 (19). However, we did not observe
leukoerythroblastosis in the whole cohort, but we noted bands and
metamyelocytes in 23% of the COVID-19 patients’ peripheral smear. We
detected the lack of concordance between LUC/DNI as measured by the
counter and manual counting. This addresses the importance to assess
peripheral blood smears.
Thrombocytopenia was detected in only one patient with aplastic anemia
and COVID-19; thrombocytosis was not noted in any patient. In a
meta-analysis, low platelet count has been associated with the increased
severity of the disease and increased mortality in adults with COVID-19,
thus serving as an indicator of worsening illness during hospitalization
(9). The absence of thrombocytopenia in our series may be related to
better clinical prognosis of the disease in children.
Zini et al. from Italy reported marked morphological abnormalities in
neutrophil lineage and platelet morphology in adults with COVID-19,
mainly very large, usually hyperchromatic platelets, both in patients
with thrombocytosis and thrombocytopenia (15). We noted some nonspecific
dysplastic changes in peripheral smear of affected children. Giant
platelets were noted in 20% of children with COVID-19. Vacuolated
monocytes, hypergranulated neutrophils and pseudo Pelger-Huet
abnormality were also seen in 13%, 7% and 30% of COVID-19 infected
children, respectively. In patients with COVID-19, upregulation of
pro-inflammatory cytokines in the blood, including interleukin (IL)-1,
IL-6, TNF, and interferon γ has been reported (5). Dysregulation of
immunological environment may have an important role in the pathogenesis
of myelodysplastic syndromes (20). We do not have the data for
pro-inflammatory cytokines in the blood and we speculate that the
dysplastic changes of blood cells in our series might be related to
those altered cytokines.
In conclusion, leukocyte and neutrophil counts were lower in children
with COVID-19 compared with children with similar symptoms. Lymphopenia
and reactive lymphocytosis, dysplastic changes of granulocytic lineage
and giant platelets on peripheral smear, although not specific, could be
noted in children with COVID-19. Further studies on hematological
findings linked with the course of the disease in children are
warranted.
Conflict of Interest: The authors have indicated they have no
potential conflicts of interest to disclose.