What Are PCR, qPCR, RT-PCR, and Their Differences?
More Programs and Publications Featuring Dr. Kyle Riding
In this program:
PCR, qPCR, and RT-PCR are three related tests. Watch as medical laboratory scientist Dr. Kyle Riding shares insight about how the tests differ and how they are used in medical laboratory diagnostics.
Transcript
Leo Hesse:
Dr. Riding, let's talk about PCR or polymerase chain reaction as it is commonly known. In the COVID era, we have heard this time a lot, can you please let the audience know what PCR is, and why is it important?
Dr. Kyle Riding:
Absolutely, so before the COVID pandemic, I'm betting a lot of viewers today may not have actually heard the acronym PCR, or if you did, it may have been in passing, but...
Let me make something very clear on the front-end, PCR is not new, it has been around since the late ‘80s when it was first characterized in research institutions in California, coincidentally. But what PCR does is essentially, if we're looking for a little segment of DNA, just one little segment of DNA that may be part of the COVID virus, that coronavirus or may be part of some malignancy that's present in a patient.
Well, just those few strands of the genetic material that we collect in that nasal swab for coronavirus patients or just those few malignant cells that may be in a blood sample for a patient with certain malignant cancerous conditions, there may not be enough of that genetic material to detect by itself. So what PCR does is it essentially puts that genetic material through an amplification process, where I think of PCR like a photocopier, we're looking for a particular DNA or RNA sequence, and we just make a ton of photocopies of it, so we can detect it more readily, and that's why it's been a really powerful tool in this pandemic, because if you have a really viral, small, low viral load of the coronavirus, this test is able to amplify that viral load and give us a really sensitive measure on if you have coronavirus at all.
Leo Hesse:
Thank you for that. You just took me back to memory lane again, Dr. Riding. I remember doing this in my undergrad and more so in my post-graduate work at the University of Nottingham. Lots and lots of work being done here in this space. Let's switch over to qPCR test and the RT-PCR tests.
Can you tell us what these are and how do they differ from the standard polymerase chain reaction test?
Dr. Kyle Riding:
Absolutely, so you may see on some of your lab reports, PCR with little letters in front of it. The first is qPCR, and the q in qPCR simply means quantify. And so it's essentially a specialized version of PCR where we don't actually just make photocopies of that genetic sequence.
We don't just amplify that genetic sequence, we count how many amplifications or how many of those copies are present in the sample, you provide us, that's qPCR. What we quantify, the other is our RT-PCR, which stands for reverse transcriptase PCR.
So some fun language in there that gets all of us, genetic folks in molecular diagnostics excited, but to understand reverse transcriptase PCR, it's important to remember how our cells work. If DNA inside the nucleus of ourselves, and for the DNA to actually exert its effect, to do its job, it needs to be made into a copy called mRNA.
So we need to take that DNA, process it via ourselves and normal mechanics into mRNA. That mRNA goes into other parts of the cell and starts producing proteins from them, so we go from DNA to RNA to proteins, it's kind of the central tenet of molecular biology.
But here's the thing, when we're looking for viruses like coronavirus...coronavirus actually has an RNA sequence as its genetic material, it's different than our own cells that use a DNA sequence to carry that genetic material from generation to generation. So what reverse transcriptase PCR does is allows us to take RNA and amplify it using these PCR techniques, so it's really useful for RNA-based viruses like coronavirus or RNA situations where we may be looking for RNA versus DNA.
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