Laboratory tests in the diagnosis of covid-19

Abstract

The gold standard for routine microbiological diagnosis of coronavirus disease 2019 (COVID-19) is quantitation of viral RNA in respiratory specimens by reverse-transcription polymerase chain reaction (RT-PCR). Detecting severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) specific IgM and IgG antibodies in patient sera are additional diagnostic tests. It has been known that virus release begins a few days before clinical signs appear, and therefore, beginning from 2-3 days before the manifestation of clinical symptoms, virus RNA can be detected in the respiratory tract during the symptomatic period of the disease. Since the viral load is higher in lower respiratory tract samples such as bronchoalveolar lavage and tracheal aspirate, PCR positivity rate might be found higher compared to nasopharyngeal samples. Confirmatory PCR tests require specific equipment and trained personnel, and they are also time-consuming and costly. Antibody assays are simple, faster tests, do not require much equipment and applicable in any laboratory. They can even be performed with 2-3 drops of blood collected from the finger tip of patients using relatively inexpensive chromatographic-rapid tests. These tests can be used in the later period of the disease since specific antibodies appear on the 7-10th day of clinical signs in patients with COVID-19. Rapid antibody card tests have an average specificity and sensitivity, while antibody tests using microELISA have higher sensitivity and specificity.