There are 4 major types of tests for SARS-Cov-2 disease. Each test will have its own sensitivity and specificity established to indicate its accuracy. Of course, there will be a number of manufacturers and their tests will have their individual levels of specificity and sensitivity for each of these types of tests.

PCR TESTING - The most common test is a molecular test that will directly test for the virus particle – all of which are considered nucleic acid amplification tests. Of the various types of these tests, the most sensitive and specific is the Reverse Transcription Polymerase Chain Reaction or RT-PCR, commonly referred to as a “PCR Test.” This is performed either as a swab deep in the nose, a swab at the end of the nose (usually performed as a dab into each nostril), or from a mouth swab or saliva spit test. These tests cannot tell if the virus particle is infective, only that it is there. This is an important distinction. For these tests to be accurate, the timing is critical.

ANTIGEN TESTING - An antigen test is also performed as a deep nasal swab, nasal swab that is not so deep, throat swab or a saliva spit test. This test detects proteins produced by the virus. There are 29 proteins that make up the SARS-Cov-2 virus. Much of the work done on test and vaccine development is against the proteins making the S spike protein (several types of them) and the capsule substance called nucleocapsid phosphoprotein N. The antigen tests will most likely be accurate from about two days before symptoms develop (4 days after exposure) to days after symptom development.

ANTIBODY TESTING - Your body starts making antibodies called IgA, IgM, and IgG within 1 to 2 weeks of the onset of infection. These antibodies will last for weeks, at least 8 and maybe detectable for much longer. These are the humoral antibodies as opposed to the cell-mediated immune response consisting of B-cell and T-cells which may well last a lifetime.

Testing for the appropriate B-cell and T-cells is exceedingly difficult and will not be available as routine tests but are an important research tool to determine how long persons will remain immune due to natural disease or immunizations.

VIRUS CULTURE - A viable virus culture means that the virus that was tested was able to reproduce when placed into experimental laboratory cells. This is the proof that the virus tested was contagious. Nasal swabs for the PCR test only identify that virus particles were found, not that the virus was capable of infection. You may remain positive for viral particles for an average of 17 days (maximum tested so far has been 83 days), while most people are probably not contagious after 10 days from onset of symptoms.

The appropriate location for taking the test changes as the virus moves through the system starting at the nose, then working its way deeper to the nasal pharynx, finally into the lungs. Nasal secretions for PCR may remain positive for an average of 17 days as mentioned above, but they may become negative long before. The actual infection is moving deeper as it continues, so even nasal swab PCR tests are frequently negative when a person is dying of severe lung infection while they may remain falsely positive when the person is immune and no longer shedding contagious virus particles (only non-viable virus particles). Properly performed, the virus culture proves infection is present.