Introduction
In December 2019, pneumonia for unknown reasons emerged in Wuhan city,
Hubei of China. Chinese scientists extracted novel Coronavirus from
patients’ specimens and named it as severe acute respiratory syndrome
coronavirus 2 on 7 January 2020 that was formerly called N-cov-20191. The World Health Organization (WHO) finally
announced the new coronavirus as COVID-19 in February 20201. Coronaviruses are a large family of viruses that
are well-known to cause a wide variety of clinical manifestations from
the mild common cold to severe forms of respiratory diseases such as
Middle East Respiratory Syndrome (MERS) and severe acute respiratory
syndrome (SARS) 2,3. The clinical manifestations of
COVID-19 vary from asymptomatic infection, mild forms of upper
respiratory tract illness, viral pneumonia, acute respiratory failure,
and death 4,5. The most common clinical features of
COVID-19 including fever, dry cough, fatigue, diarrhea, severe muscle
pain, and pneumonia that lead to Acute Respiratory Distress Syndrome
(ARDS), metabolic acidosis, septic shock, thrombosis, and heart failure,
renal failure, and liver disease 6,7. Although the
mild form of COVID-19 can be treated by appropriate medical
interventions, the most severe cases especially the elderly who
experience underlying medical conditions develop severe illness and
increase the mortality rate 8. Older adults with
pre-existing medical conditions such as diabetes, asthma, and
cardiovascular disease may be more vulnerable to COVID-199. The recognition and discrimination of severe
COVID-19, mild infection, and asymptomatic form are clinically vital10. The most important laboratory findings in COVID-19
patients are low concentration of albumin (75.8%), high serum
C‐reactive protein (CRP) (58.3%), ESR (41.8%), LDH (57%), and
lymphopenia (43%) 11. Lymphopenia was detected in
severe COVID-19 patients (85%) and suggested as a severity predictor;
the average count of lymphocytes of Intensive Care Unit (ICU) -
hospitalized patients was 800 12. Lymphopenia could
have occurred in COVID-19 patients via four mechanisms: a) viral
attachment to the cell surface receptor ACE2, infect lymphocytes that
lead to lymphocyte death 13; b) the possible role of
coronavirus in the destruction of lymphoid organs 14;
c) induction of lymphocyte apoptosis by the production of TNF-α and IL-615 and d) inhibition of lymphocyte production during
metabolic acidosis 16. Although the pathogenesis of
COVID-19 remains unclear, lymphopenia was observed in most of the
patients 17. Aging and chronic illness lead to
endothelial dysfunction that dismounts cell-cell adhesions, promotes
endothelial cell death, extravasation that resulted in lymphopenia18. The infection of COVID-19 is diagnosed and
confirmed by Real-Time PCR (RT-PCR) and gene sequencing of the blood and
lung samples. In the early phase of the disease, positive nasopharyngeal
RT-PCR results ranged between 30- 60% 19. In
emergency cases, the low sensitivity of RT-PCR misses diagnoses of
COVID-19 patients failed receiving appropriate medications and upended
outside spreading of COVID-19. In contrast with RT-PCR, chest computed
tomography (CT) has sufficient sensitivity for atypical radiographic
manifestations of COVID-19 cases who are asymptomatic and/or negative on
the initial RT-PCR test 20,21. According to the
Chinese reports, chest CT is adequately sensitive (97%) in early
detection of COVID- 19 patients compared with RT-PCR22. Bilateral lung involvement was observed in 98% of
patients and lobular and subsegmental areas of consolidation were
considered as the most typical findings of CT 4.
Besides, several COVID-19 cases demonstrated ground-glass opacities
(GGO) and pulmonary consolidation with round morphology23. The main CT findings of COVID-19 pneumonia are the
shape of GGO, crazy paving pattern, and Consolidation24.
Iran is one of the worst affected countries by the coronavirus and
Mazandaran province is considered one of the most impacted areas25. The paucity of evidence on the relationship
between lymphopenia, chest CT examination, and mortality rate in
COVID-19 patients made us ascertain this possibility. Since Imam
Khomeini hospital in Mazandaran was considered as the main referral
center for the management of COVID-19 cases, we aim to retrospect and
evaluate the lymphopenia in COVID-19 patients and its association with
lung involvement.