Immunity and inflammatory biomarkers in COVID‐19: A systematic review

Summary Coronavirus disease 2019 (COVID‐19) is a clinical syndrome caused by the severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) virus. Patients can be asymptomatic or present respiratory and gastrointestinal symptoms, and even multiple‐organ failure which can lead to death. The balance between an effective antiviral response and dysregulated immune response is the key factor determining the severity of COVID‐19 progression. A systematic review was performed using the NCBI‐PubMed database to find the articles related to COVID‐19 immunity and inflammatory response published from 1 December 2019 to 15 April 2020. Haematological, immunological and biochemical parameters were extracted and correlated with disease severity, age and presence of comorbidities. Twelve articles were analysed comprising a total of 1042 hospitalized patients infected with SARS‐CoV‐2 and 95 different parameters. Total lymphocyte count and levels of CD3+ and CD4+ T cells were decreased in severe and critical cases. Neutrophilia was found in patients who progressed to acute respiratory distress syndrome (ARDS). Interleukin‐six (IL‐6) was high in mild and severe patients regardless of comorbidities. Erythrocyte sedimentation rate (ESR) and count and C‐reactive protein (CRP) levels were increased regardless of disease severity or presence of comorbidities. High levels of D‐dimer and lactate dehydrogenase were present in diabetic patients and patients who developed ARDS. Procalcitonin levels were elevated to varying degrees in severe and critical patients. We conclude that the total lymphocyte count, CD3+ and CD4+ T cells are low, especially in severe and critical COVID‐19 patients; ESR, CRP and IL‐6 were elevated, independent of the severity of disease. Understanding the inflammatory response of COVID‐19 patients is essential for the development of better therapeutic and management strategies.