As the world faces the Coronavirus pandemic testing has become a hot issue that people are facing in their daily lives.  But the question remains, which test is best?  It is likely that we will never know the answer to that question, but an understanding of the options available can certainly help the general public to make an informed decision before selecting a method of testing.  According to the article from the Financial Times, titled “What coronavirus test does the world need to track the pandemic?” there are two main types of tests for the virus officially named Sars-CoV-2: Antigen tests and Antibody tests. Antigen tests are used to detect whether or not an individual is infected with the coronavirus that causes Covid-19 while antibody tests are used to determine if an individual has been infected in the past.

Antigen tests come in two varieties, a rapid version that delivers results in minutes and another using Polymerase Chain Reaction (PCR) to multiply the genetic material found in a virus containing sample from an infected individual which takes longer.  Both the rapid and the PCR tests can be performed on a sample collected using a nasopharyngeal swab but can also be done using a throat swab or saliva sample.

Antigen Testing via Nasopharyngeal Swab

The virus can be detected as early a the first day of symptoms but is most accurate in the first week.  This is measured by the cycle threshold where the lower values indicate positive results.  No tests are always accurate but the rapid tests have been found to have more false positive and negative results than the PCR tests.  In a study performed by Vermont’s Department of Health only four individuals of 65 who had tested positive with the rapid test, also tested positive with the PCR test.  Because of this many states require both tests to confirm a positive diagnosis.  Unfortunately, the PCR tests have also shown high incidences of false negatives.  Regardless of which test is used, the accuracy still seems to be connected to the manufacturer of the test itself. Since the PCR test is thought to be the most accurate because it detects the presence of the genetic material of the virus, it is less likely to provide a false positive.  As result, these are best used to identify infection as opposed to letting an individual know that they are not infected.

Antibody tests require a blood sample in order to detect the presence of antibodies against Sars-CoV-2 because once an individual is infected with the virus their immune response creates IgM antibodies that are present close to the time of infection and IgG antibodies that are produced longer after infection.  These antibodies are proteins produced by the white blood cells that help to fight the virus, so if they are present in an antibody test, is clear that the individual has already been infected.  When an individual is infected with a virus, lymphocytes called B cells are triggered by the presence of the antigen of that virus, and bind to the antigen using an antigen receptor.  This then causes the production of cells that produce proteins called antibodies which have the same shape and structure as the antigen receptors of the B cells making them helpful in directly defending against antigens present in body fluids. Antibody tests provide a quick result and are preferred because they help people to determine if a person can return safely to society with less risk of infection.

As the pandemic became a global issue many tests began to be developed but the antigen tests were more commonly performed in the public while the antibody tests were reserved for private companies due to the need for more materials like swabs and reagents to perform the tests.  Both tests are being created all over the world but some countries are producing more than others and the US was slow to get started but has increased production more recently. Because the tests must be of good quality, and the staff that are using them must be trained well, it is hard to produce them fast enough.