False Positives in PCR – a Primer
This is an explanation of false positives in qRT-PCR: what they are and how they occur. qRT-PCR is the type of PCR used to test for COVID-19 and it stands for 'Semi-Quantitative Reverse Transcriptase-Polymerase Chain Reaction' (a bit of a mouthful, so sometimes people just say 'The PCR test'). To unpack qRT-PCR and understand its use(s), we need to step back and think about genetic information and PCR in the round. Your genes and how PCR amplifies tiny amounts of DNA The genetic information of many species is made of DNA. This is true (as far as we know) for all bacteria, fungi, protozoa, plants, insects and vertebrates, including you. If you need to study the DNA from a small sample of one of these, you can amplify part of it using PCR (polymerase chain reaction - we'll come to the 'RT' part in a minute). This is shown in Figure 1a. PCR is incredibly sensitive. It can start with as little as a single DNA molecule and quickly (in a couple of hours) amplify part of it to produce billions and billions of copies - enough to study in depth. PCR is used widely in research, clinically and in forensic medicine: genomic DNA in a tiny blood stain can be amplified by PCR so that investigators can combine it ...
