Blood-based biomarkers for diagnosis, prognosis, and severity prediction of COVID-19: Opportunities and challenges.

The reasons for high morbidity and mortality with Corona virus disease (COVID-19) disease remain unanswered with extremes of manifestation and uncertainty of modes of transmission for which biomarkers are urgently needed for early prediction of severity and prompt treatment. We have reviewed publications from PubMed (years 2019-2021) analysing the biochemical, immune-inflammatory, nucleic acid, and cellular biomarkers that predict infection, disease progression in COVID-19 with emphasis on organ-specific damage. Our analysis of 65 biomarkers assessing the impact of SCoV-2 infection on five organs (lung, liver, cardiac, kidney, and neural) reported that increased levels of CRP, TNF-α, ferritin, IL-6, D-dimer, Procalcitonin, Fibrinogen to Albumin Ratio (FAR), and decrease platelet count (PC), lymphocyte count, leukocyte count, and CD4/CD8 ratio shows promising association in the early diagnosis, prediction of prognosis and severity disease and also correlates with cytokine storm a cardinal feature of COVID-19 progression. In the above scenario, this review has put forth the most promising biomarkers for COVID diagnosis and prognosis based on the reported literature. In recent year's chemically synthesized antibody-like biomolecules, aptamers were also used in the diagnosis of COVID-19 which could be preferably used for diagnosis over antibodies. Biomarkers including increase in free DNA and Fibrinogen-to-Albumin Ratio, CRP, PCT, and Ferritin along with a consequential decrease of CD3 T, CD4 T, CD8 T, NK cells with corresponding increase in CD4+/CD8+ ratio following SARS CoV-2 infection has been consistently correlated with disease severity. Despite the two waves of COVID-19 pandemic, currently there is no standard clinical practice guideline for evaluating the severity of the devastating pandemic of COVID-19, hence these biomarkers will have immense relevance for the third and subsequent wave of COVID-19 and related pandemic.