Several methods have been developed in order to diagnose COVID-19 disease, which is caused by the new coronavirus (SARS-CoV-2). Most methods detect either viral parts or human antibodies from the sample. Assay specificity is crucial, because other coronaviruses exist – causing less severe respiratory illnesses.
Detecting genetic material in the sample (PCR)
The whole genome of the new coronavirus has been sequenced. Newly developed assays are based on this known genetic sequence, and are able to detect if the sample contains one or more target genes of this virus.
A positive result of the assay indicates an ongoing virus infection and potential cause of patient’s symptoms. Using more than one target gene confirms, that the virus at hand is specifically SARS-CoV-2.
Detecting structural parts in the sample (antigenes)
Genetic material of virus is covered with viral envelope structures. Some methods are targeted against these structural parts of the virus and find out, if the sample contains SARS-CoV-2 specific structures.
A positive result from also these assays indicates, that the virus is likely infecting the patient. The assay needs to be targeted to the unique structural parts of this virus. It should recognize only SARS-CoV-2, not any other similar viruses.
Detecting human antibodies in the sample (antibodies)
When subjected to viral infection, in couple of weeks human body starts to produce antibodies in order to overcome the disease. Some new tests are designed to detect human antibodies formed against SARS-CoV-2.
A positive result from these assays means, that the person has encountered the virus at some point in their past – these assays are not for detection of acute viral disease. The specificity of these assays is very important: they need to show, if a person has had the COVID-19 disease induced by SARS-CoV-2 and not some other disease caused by some similar virus.
