What is a PCR test? Let's talk about it simply!

When we hear the word PCR, we think of the Covid pandemic, right? The time when we had to stick a swab in our nose and wait for the report to come... that will never be forgotten. But did you know that PCR is not just used to detect Covid? This is actually a very important test that has made a huge breakthrough in medical science. So today, let's talk about what this PCR test is, what other things can it detect, and how it works in a simple way that you can understand.

What is PCR simply?

Okay, let's put it this way. Imagine you had to find a single word on a single page of a single book, out of thousands of books in a large library. How difficult would that be? It's like finding a tiny piece of DNA or RNA , the genetic material inside the cells in our bodies.

PCR (Polymerase Chain Reaction) technology makes that difficult task easier. What this does is copy the smallest piece of DNA or RNA we are looking for hundreds of thousands, even millions of times (amplification). It's like finding the page with the word in the library book, putting it in a photocopy machine, and making about a million copies. Then, since that difficult-to-find word is now everywhere, we can easily identify it.

Simply put, PCR is a test that takes a very small amount of a cell from our body, a drop of blood, or a nasal swab, and artificially grows a specific piece of DNA or RNA in it in a laboratory to confirm whether it is present in our sample or not. This is a very sensitive test. This means that it can detect even very small amounts of the virus. This method belongs to a group of tests called Nucleic Acid Amplification Test (NAAT).

What diseases can be detected by PCR testing?

Although PCR has become popular due to the COVID pandemic, it has been used in the medical world for decades. There are many things that can be detected with this test. Let's look at some of the main ones.

How do you take a sample for a PCR test?

The way you take a sample for a PCR test depends on what kind of disease you are looking for. The method of taking a sample is different for each condition.

Most of the time, you don't need to do anything special to prepare for a PCR test. However, in some cases, such as when doing something like a biopsy, your doctor will give you the necessary instructions beforehand.

How does PCR technology work?

Okay, now let's see how this amazing technology actually works. This is a bit scientific, but I'll explain it simply.

1. Sample preparation: First, DNA or RNA is isolated from the sample (blood, secretions, etc.) taken from you.

2. Making the mixture: Next, this isolated DNA/RNA is mixed with some special chemicals. The main thing in this mixture is an enzyme called DNA Polymerase . This is the main one that does the photocopying work.

3. Heating and Cooling Cycle: Now the small tube with this mixture is placed in a special machine. This machine raises and lowers the temperature very quickly.

• Denaturation: First, the temperature is increased to about 95 degrees Celsius. This causes the two DNA strands to separate.
• Annealing: Next, the temperature is lowered to about 55 degrees. Then, small pieces of DNA (primers) that match the DNA fragment we are looking for are attached to the separated DNA strands.
• Reheating (Extension): Then the temperature is raised to about 72 degrees. Then the DNA polymerase enzyme comes in and makes a new DNA strand from that primer that matches the original DNA strand.

4. Copying: Now two copies of one DNA strand have been made. This temperature cycle repeats itself about 30-40 times. In one cycle, the amount of DNA doubles. Two becomes four, four becomes eight, eight becomes sixteen... After about 30 cycles, more than a billion copies have been made from the original single piece of DNA.

Now, that DNA/RNA fragment, which was previously too small to detect, has become large enough to be easily detected.

Are there types of PCR tests?

Yes, there are mainly two types that we need to be aware of.

• Reverse-transcriptase PCR (RT-PCR): Some viruses, such as Covid, influenza, and HIV, have their genetic information in RNA rather than DNA. Normal PCR can only copy DNA. So, what you do in RT-PCR is first use a special enzyme (`Reverse Transcriptase`) to 'convert' that RNA into DNA. The resulting DNA is called complementary DNA (cDNA). Then the normal PCR process takes place.

• Real-time PCR / Quantitative PCR (Q-PCR): This is a slightly more advanced method. What happens in this is that as the DNA is copied, a fluorescent label is attached to it. As the amount of DNA copied increases, this fluorescence also increases. The machine can measure this fluorescence. So, while we are waiting, that is, in real-time , we can see whether the relevant DNA is present in the sample or not. Not only that, it can also give a rough idea of ​​how much virus was in the original sample (viral load). A Real-time RT-PCR test that combines both of these methods is often used to detect Covid.

What does the PCR report mean?

It is very important to understand a PCR report when you receive it.

• Detected / Positive: If your report says "Detected" or "Positive," it means that your sample contained parts of the virus or genetic material they were looking for. Simply put, you probably have the infection.

• Not Detected / Negative: This means that the relevant DNA/RNA fragments could not be found in the sample tested. This means that you most likely do not have that infection.

How long it takes to get results varies depending on the test being done. Nasal swabs (like COVID, influenza) usually get results within 24 hours. However, blood tests and biopsies to look for genetic diseases can take a week or more.

If you have any questions or concerns about a PCR test or its results, be sure to talk to your doctor about it.