When the infection first started in China, it took several weeks to detect Novel Coronavirus. As the clinical features were similar to SARS-CoV infection, tests were performed to identify SARS-CoV. Soon, it was recognized that the new virus is not precisely SARS-CoV but a similar virus belonging to coronavirus family. COVID-19 became a pandemic in a short duration of time. Several biotechnology companies started developing tests for COVID-19. There has been an acute shortage of tests all across the globe. There is not much research on these tests as the pandemic spread in no time.
The technique used to detect Novel Coronavirus is Reverse Transcription Polymerase Chain Reaction (RT-PCR). Samples are taken from nose, throat or sputum and RT-PCR is performed. A study published in European Journal of Radiology, included a total of 36 patients with confirmed COVID-19 pneumonia. Using the RT-PCR test, only 30 patients tested positive and 6 were missed initially. 3 became positive on the second test and the other 3 became positive on the third test. 35 of these patients had abnormal CT findings at the time of presentation and only 1 patient had a normal CT scan. Based on this study, the ability of COVID-19 test to detect a true positive infection (sensitivity) is only 83.3%. Abnormal CT scan has a sensitivity of 97.2%.
Another study from the journal Radiology included 51 patients in the study. RT-PCR test was found to have a sensitivity or the ability to detect true positive infection of only 71%. CT scan was found to have a higher sensitivity of 98%. The study stated the possible reasons for the low efficiency of the testing include 1) immature technology 2) variation in detection rate from different manufacturers 3) low viral load in the patient or 4) improper clinical sampling.
It is apparent that COVID-19 test is only 70%-80% accurate. It means that 30 out of 100 patients may have a false result. Even though studies with more patients are required to validate these results further, accuracy of the test remains concerning. If the affected people have classic signs and symptoms of COVID-19, they should be isolated even if the test results are negative. Multiple tests may be required to confirm the test. A concomitant CT scan of the chest helps to diagnose COVID-19 as CT scan accuracy is much higher than COVID-19 test.
Long C et al. Diagnosis of the Coronavirus disease (COVID-19): rRT-PCR or CT? Eur J Radiol. 2020 Mar 25;126:108961. doi: 10.1016/j.ejrad.2020.108961.
Fang Y et al. Sensitivity of Chest CT for COVID-19: Comparison to RT-PCR. Radiology. 2020 Feb 19:200432. doi: 10.1148/radiol.2020200432.