A Review on the diagnostic approaches of COVID-19 infection; Features and limitations

Detection of coronavirus disease 2019 (COVID-19) in early stage is indispensible for outcome improvement and interruption of transmission chain. Clear understanding of the nature of the diagnostic tests for severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) and their challenges, collecting the most diagnostically valuable specimen at the right time from the right anatomic site, and interpretation of their findings is important. This review scrutinizes current challenges and interpretation of reverse transcriptase polymerase chain reaction (RT-PCR), as the reference method, loop-mediated isothermal amplification (LAMP), antibody and antigen detection, typical lung imaging characteristics and prominent abnormal changes in laboratory findings of patients with proven COVID-19, and describes how the results may vary over time. Bronchoalveolar lavage fluid and sputum specimens demonstrate the highest positive rates (93% and 72 %, respectively) in molecular diagnosis of COVID-19. Alternatively, repeated RT-PCR assays can be performed; as over time, it is an increase in the likelihood of the SARS-CoV-2 being present in the nasopharynx. Combining clinical evidence with results of chest computed tomography (CT) and RT-PCR can minimize the risk of diagnostic errors. Elevated levels of interleukin 6 (IL‐6) and D-dimer are thought to be closely associated with the occurrence of severe COVID‐19 in adults, and their combined detection can serve as early factors predicting the severity of COVID‐19. Moreover, elevated acute phase proteins are associated with a poor outcome in COVID-19. Serological diagnosis also is an important tool to understand the extent of COVID-19 in the community, and to identify individuals, who are immune. Antibodies begin to increase from the second week of symptom onset