There are two methods used in diagnostic testing: antigen and RT-qPCR. I know that antigen and antibody sound similar, and they're easy to get mixed up. The reason they sound similar is that they're related. An antigen is a small part of a pathogen (foreign body) that an antibody recognizes and holds on to. The antigen is essentially the key in the lock of the antibody, where each antibody recognizes a single, specific antigen, and is able to hold onto that antigen when the two come into contact.

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Here's an easy way to remember: B holds G. The antiBODY holds the antiGEN. If you're slightly more visual, on the right there's a picture of a guy we'll call Bruce, holding the letter G. again, B holds G. If you're a big fan of 7/11, you could remember Big Gulp. Whatever works for you. For a more accurate and scientific visualization, see directly below Bruce for what an antibody-antigen complex looks like.

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Our other diagnostic test is RT-qPCR, a.k.a. Reverse Transcriptase quantitative Polymerase Chain Reaction. Phew, I got winded just reading that! We'll get into what all of that actually means later, so we'll just establish some basic understanding for now. RT-qPCR takes virus RNA, turns it into DNA, and replicates the DNA to produce a lot of it. In a RT-qPCR test, a sample is taken from a person and put through this process. Scientists then look for new DNA generated by this process, and if they find it, they know the sample contained virus RNA, meaning the person was infected.