Well, I have been educated about covid-19 tests. The media talks a lot about the PDR test and calls it the gold standard. What i never mentioned is there are 2versions, one of which is not accepted by Canada but is by the US..
Question: What is the reason for making it so difficult?
There are PCR and there are antigen (AG) tests. Both require nasal and/or throat swab. The difference between them is how the extracted sample is processed and analyzed (and the time it takes to get the result).
Basically AG just looks for the virus at the swab sample, while PCR multiples and reproduces and remultiplies the sample to show if there is the virus or not. That's why it needs the special reactive because it's basically a lab multiplication of the swab culture.
Also a very small viral load (early stages of infection, or simply a small virus presence in the body) will not show on AG (certain threshold of virus volume need to be reached) for AG test to come back positive, but on PCR even one tiny virus unit would show because of the remultiplication process of the swab culture.
That's why AG (rapid) tests are not valid form of test for entry procedures, because they do not detect very small values of virus presence. There are some new AG tests which claim they are eon par with PCR tests in detection thresholds, but only time and checks will show of the manufacturers really developed an antigen equivalent to PCR tests.
Meanwhile, RT-LAMP (also reactive based) and TMA are on the forefront of quick testing with PCR reliability. RT-LAMP is spreading internationally, while I only heard of Spain currently doing TMA tests.