Let's learn about the PCR test simply, just like from a friend!

You may remember that during the Covid-19 pandemic, we all talked about the PCR test . Some people must have been a little scared, thinking about a stick inserted into the nose? But what exactly is this PCR test? Can it only detect Covid-19? No, PCR is a very important test method in medicine that helps with many things. Let's talk about all this today, simply and clearly, as if we were talking to a good friend.

What is PCR? Can you explain it a little?

Simply put, PCR is an abbreviation for Polymerase Chain Reaction . It is used to detect genetic material in our bodies, either DNA or RNA . Imagine a small sample taken from you, it could be a drop of blood, or a swab from the inside of your nose. That tiny piece of DNA or RNA in that sample is taken and millions, maybe billions, of copies are made in the lab. This is what scientists call amplification , which means "increasing" or "multiplying." It's like making many copies of a single sheet of paper with a photocopier.

By making many copies like this, it becomes easier for scientists to study the DNA or RNA in the original small sample and see if there is anything special in it. PCR belongs to a group of tests called Nucleic Acid Amplification Tests (NAAT) .

Although many people have heard the word PCR in connection with Covid-19 testing, this technology has been used in the medical field for a long time and is a very useful method.

What can be detected by PCR?

Now let's see what kind of things this PCR test can detect. Many people think it's only for Covid-19. But that's not the case. Take a look:

• Infectious diseases: PCR can help determine whether a fever, cold, or cough you have is caused by a virus , bacteria , fungus , or parasite . For example:
• The SARS-CoV-2 virus that causes COVID-19 (COVID-19) .
• Influenza , that's what we commonly call the flu.
• Respiratory Syncytial Virus (RSV), which is especially common in young babies.
• The bacteria that causes tuberculosis.
• Many other viral and bacterial infections.
• Genetic diseases: Some people have genetic diseases that they are born with, right? PCR is also used to detect conditions like Cystic Fibrosis , Huntington's Disease , and Fragile X Syndrome . These are very complex conditions, so early detection is very important for treatment.
• Types of cancer: This method also helps to identify certain types of cancer, such as lymphoma .
• Gene changes in cancer: When treating a person with cancer, this PCR test can also detect specific gene variations/mutations in those cancer cells. This will allow targeted therapy to be used to target those specific changes. This is a major advance in the field of cancer treatment.
• Future disease risk: People with certain genetic changes may be at higher risk of developing serious diseases like cancer in the future. This PCR is also used for genetic testing for cancer risk . This allows you to be aware in advance and make lifestyle changes if necessary, or to stay vigilant by getting tested regularly.
• Prenatal testing: PCR is also helpful in tests performed to see if a pregnant woman's unborn child has a genetic condition.

Not only this, you may have seen it in movies, where DNA evidence, such as a tiny hair or a bloodstain found at a crime scene, is taken and used to identify the criminal. Forensic labs also use this PCR technology to increase the amount of DNA and conduct tests.

What are the tests and methods that use PCR technology?

PCR technology is used in a variety of testing methods. The type of test you need to take a sample for will depend on what you are testing for. Here are some examples:

• Blood tests: A blood sample is taken and PCR is used to detect genetic changes and certain infectious diseases.
• Nasopharyngeal swab: A mucus sample taken from the inside of the nose or throat can be used to test for respiratory infections like influenza (flu), COVID-19, and RSV. This is what we have all experienced during COVID.
• Preimplantation Genetic Diagnosis (PGD) or Preimplantation Genetic Screening (PGS): During the In Vitro Fertilization (IVF) process, a few cells from the embryos are taken and tested for genetic conditions before they are implanted in the mother's uterus. This is usually done a few days after egg retrieval.
• Amniocentesis: During pregnancy, a small amount of amniotic fluid surrounding the baby in the mother's womb can be removed and PCR can be used to test the baby's genetic status. This is a test performed by a specialist doctor.
• Biopsy: To identify genetic mutations in cancer cells (molecular testing), a small sample of the tumor (tumor biopsy) or a bone marrow biopsy is taken. This is like a minor surgery. The sample is then used to perform PCR to look for genetic changes.

How do you prepare for this test?

In most cases, no special preparation is required for a PCR test. However, it depends on what you are testing for and what method is used to collect the sample. For example, some blood tests may require you to fast for a few hours before. So, it is best to ask your doctor or the testing facility if there is anything special you need to do.

How does PCR work? A little science!

This is a bit of a scientific story, but let me explain it simply. What PCR does is to identify a sequence that is unique to the DNA you want to look for, that is, specific to it. This sequence could be a specific genetic change in a cancer, or it could be the genetic code of a virus or bacteria. This is called target DNA .

The name "Polymerase Chain Reaction" refers to the process by which a large number of copies of a target DNA are made (amplified) in the laboratory. This process uses an enzyme called DNA polymerase . This enzyme makes copies of the target DNA, if it is present in the sample.

This "chain reaction" occurs when a solution goes through many cycles of heating and cooling. In one cycle, the amount of DNA can double. Think of it as one to two, two to four, four to eight... and so on, eventually making millions of copies. The advantage of this is that PCR can detect even small amounts of DNA or RNA that would otherwise be missed by other tests.

Often, after PCR is done, scientists have to do more tests to analyze the amplified DNA. But sometimes, special labels are added to the solution during the PCR process, which can tell whether the sample is positive or negative. This method can be used to quickly get results, especially when looking for infections like viruses.

What types of PCR are there?

There are different types of PCR. Some require additional steps to copy or analyze the DNA. Let's look at two main types:

1. Reverse-Transcriptase PCR (RT-PCR)

Imagine that the genetic information we want to copy and search for is not in DNA, but in RNA. (For example, the Covid-19 virus has RNA). Then, in this RT-PCR , what is done is that the RNA is first converted into DNA using a special enzyme (reverse transcriptase). The DNA that is formed is called complementary DNA (cDNA) . After that, the normal PCR process mentioned earlier is done. Because, normal PCR can only be done on DNA.

2. Real-time PCR / Quantitative PCR (Q-PCR)

What happens in this is that as the DNA copies are made, special fluorescent labels are added to it. These labels emit light when they bind to the target DNA. Then, without additional testing, those doing the test can see in real-time whether the relevant DNA is present in the sample. Not only that, they can also get a quantitative idea of ​​how much is present.

The confusing thing is, some people also call this "RT-PCR". But it is not the same as Reverse-Transcriptase PCR mentioned earlier. Also, this Real-time PCR method can be used in combination with the Reverse-Transcriptase PCR mentioned earlier. Then it is called Real-time RT-PCR (real-time RT-PCR) . This real-time RT-PCR method is used for nasal swab tests to detect RNA viruses like Covid-19 and influenza.

What do the results of a PCR test tell us?

When you get the results of a PCR test, the wording may be slightly different, depending on what you were tested for.

• Generally, if your result says "detected" or "present," it means that you have the genetic mutation or infection that the test looked for.
• If the result says "not detected," it means that the test was unable to find the target DNA or RNA that was being tested. However, in the case of an infection, this can sometimes mean that you tested too early in the infection process. You may still have the infection, but there may not be enough of the virus or bacteria to be detected by PCR at that time.

How to interpret Covid-19 PCR results?

This is something that many people are familiar with now.

• A positive COVID PCR result - meaning your report says "Detected" - means you are likely infected with COVID-19 , or you have recently recovered from COVID-19 (sometimes PCR can remain positive for some time after recovery).
• If you get a negative ("Not Detected") COVID PCR result , it means that you most likely did not have COVID-19 when you took the nasal swab. However, as I mentioned earlier, sometimes, early in an infection, especially if you are asymptomatic, PCR tests can be negative. So if you are symptomatic, your doctor may advise you to get tested again in a few days.

How long does it take to get PCR results?

This also varies depending on the test being performed.

• Nasal swab tests for common viruses like influenza and COVID-19 usually take a few hours or a day to produce results.
• Genetic tests that use blood tests and biopsy methods can take a week or more to get results because the analysis process is a bit more complex.

When do you need to see a doctor?

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

The most important message to take home

Although the words "PCR test" suddenly entered our daily conversation with the 2020 COVID-19 pandemic, it is actually a very valuable technology that doctors have been using for decades. PCR helps to identify and copy tiny amounts of DNA or RNA, which can be used to diagnose a variety of health conditions.

While this is common for doctors, it may not be common for you to have a test. We understand that. But the best thing is that it only requires a small sample of your body, and the procedure usually takes just a few minutes. If you have any questions, concerns, or doubts about this, please talk to your doctor. They will explain everything to you. Stay healthy!

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