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A quick thread on COVID-19 diagnostics available now and what a negative or positive test result means in reference to the different tests being conducted to detect COVID-19.
First definitions
Antigen: a toxin or foreign substance that induces an immune response from the body especially antibody production can be from a virus, bacteria, fungus basically any foreign substance
Antibody: A protein the body produces in response to an antigen
Antigen: a toxin or foreign substance that induces an immune response from the body especially antibody production can be from a virus, bacteria, fungus basically any foreign substance
Antibody: A protein the body produces in response to an antigen
There are different types of antibodies but for today's discussion we will just talk about IgM and IgG .
RNA: ribonucleic acid this is present in all cells used to control processes like protein synthesis but in viruses RNA may be used as their primary genetic material.
RNA: ribonucleic acid this is present in all cells used to control processes like protein synthesis but in viruses RNA may be used as their primary genetic material.
There are 3 different types of tests being used widely to test for COVID-19 at the moment
1. Antibidy tests detecting mainly ANTIBODY (IgG or IgM)
2. Antigen tests detect the VIRAL ANTIGEN
3. RT-PCR detect VIRAL RNA
1. Antibidy tests detecting mainly ANTIBODY (IgG or IgM)
2. Antigen tests detect the VIRAL ANTIGEN
3. RT-PCR detect VIRAL RNA
A positive ANTIBODY test for IgG means that you have currently or have had in the past a COVID-19 infection. An IgM positive test means you most likely have an acute COVID-19 infection though IgM may persist in your body even after you are out of the acute phase of the infection.
It is difficult to determine how to treat a patient with a positive antibody test because you do not know if the person still has the infection or they are recovering from it and had it previously. So this test is mostly used to determine community prevalence of an infection.
Next ANTIGEN tests detect an actual protein present on the COVID-19 virus these are the rapid tests many people are getting now. A positive from this test means that you have an active COVID-19 infection.
This tests limitation is that it is not as sensitive as RT-PCR. Most people are positive mainly in the acute phase when you have a very high number of viruses in your body so sometimes when your viral load is low and the test will not detect antigen but you may still be infected.
Think about it like looking for a needle in a haystack if there is only one you may look through the haystack all day and not find anything because your ability to detect the needle using sight isn't good but if there are 10000 needles in the haystack you are likely to find one.
