Background: Since its first emergence in Wuhan city, China, severe acute respiratory syndrome coronavirus 2, which is responsible for the
pandemic COVID‑19, has become a significant health problem all over the world affecting over 2.1 million people globally. Methods: The
current study aimed to investigate serum levels of interleukin 6 (IL-6), ferritin, C-reactive protein (CRP), lactate dehydrogenase (LDH), D-dimer
as well as lymphocytes and neutrophils count in COVID-19 patients, and to clarify the correlation of these parameters with disease severity
and progression. For these purposes, (100) patients with COVID‑19 (confirmed by polymerase chain reaction) and (20) apparently healthy
people (with matched age and sex) were included in the current study and considered as a control group. Results: All study population (patients
and control) were subjected to the evaluation of serum levels of IL-6, ferritin, CRP, LDH, D-dimer, as well as lymphocytes and neutrophils,
count. COVID‑19 patients showed a significant elevation in the levels of all parameters included in this study when compared with healthy
controls. We also found that all of IL‑6, ferritin, CRP, LDH, D‑dimer are significantly associated with the severity of the COVID‑19 symptoms.
Conclusion: Lymphopenia and increased neutrophils were also effectively correlated with disease progression. In line with these results, we
concluded a proportional correlation between the aforementioned parameters and COVID-19 suggesting the uses of these tests to the diagnosis
of critical cases.