PCR Testing

What are PCR tests?

PCR tests are a quick and very accurate way to diagnose certain infectious diseases and genetic changes. The tests work by finding the DNA or RNA of a pathogen (pathogenic organism) or abnormal cells in a sample.

• DNA is the genetic material that has instructions and information for all living things.

• RNA is another type of genetic material. It includes information that has been copied from DNA and is involved in making proteins.

Most viruses and other pathogens have DNA or RNA.

Unlike many different tests, PCR tests can find evidence of disease in the early stages of infection. Other tests may miss early signs of illness because there aren't enough viruses, bacteria, or other pathogens in the sample, or your body hasn't had enough time to mount an antibody response. Antibodies are proteins produced by your immune system to attack foreign substances, such as viruses and bacteria. PCR tests can detect disease when there are only a very small number of pathogens in your body.

During a PCR test, a small amount of genetic material in a sample is copied many times. The copying process is known as amplification. If there are pathogens in the sample, magnification will make them much easier to see.

Other names: polymerase chain reaction, rtPCR, reverse transcription PCR, qPCR, quantitative PCR, real-time PCR

How are they used?

PCR tests are used to:

• Diagnose certain infectious diseases.

• Recognize a genetic change that can cause disease.

• Find a small number of cancer cells that might be missed by other types of tests

How do they work?

PCR tests work by:

• Take a sample of blood, saliva, mucus or tissue

• The sample will contain your own DNA and possibly DNA from a pathogen or cancer cell.

• The sample is placed in a special machine. An enzyme called polymerase is added to the sample. This causes the sample to produce copies.

• The copying process is repeated several times. After about an hour, billions of copies are made. If a virus or pathogen is present, it will be indicated on the machine.

Some viruses, including COVID-19, are made of RNA instead of DNA. For these viruses, RNA must be converted into DNA before copying. This process is called reverse transcription PCR (rtPCR).

Both PCR and rtPCR check for the presence of a pathogen. Another type of PCR known as quantitative PCR (qPCR) counts the amount of pathogens in the sample. qPCR can be performed at the same time as PCR or rtPCR.

What happens during a PCR test?

There are different ways to obtain a sample for a PCR test. Common methods include blood tests and nasal swabs.

During a blood test, a healthcare professional will take a sample of blood from a vein in your arm using a small needle. After the needle is inserted, a little amount of blood will be collected in a test tube or vial. You may feel a slight sting as the needle goes in or out. It usually takes less than five minutes.

A nasal swab can be taken from the front of your nostrils (anterior nostrils). It can also be taken from the back of the nostrils, in a procedure known as a smear from the middle turbinate (MTN), or nasopharynx, the upper part of the nose and throat. In some cases, a health care provider will ask you to take an anterior nostril test or an NMT swab.

During an anterior nostril test, you will begin by tilting your head back. Thus, you or the provider:

• Gently insert a cotton swab into your nostril

• Turn the swab upside down and leave it in place for 10-15 seconds.

• Remove the swab and insert it into your second nostril

• Clear the second nostril using the same technique

• remove the swab

During an NMT swab, you will begin by tilting your head back. Thus, you or your provider:

• Gently insert a cotton swab deep into your nostril, pushing it in until you feel it stop.

• Rotate the swab for 15 seconds

• Remove the swab and insert it into your second nostril

• Clear the second nostril using the same technique

• remove the swab

During a nasopharyngeal swab:

• You will throw your head back.

• Your healthcare provider will insert a swab into your nostril until it reaches your nasopharynx (the upper part of your throat).

• Your provider will rotate the swab and remove it.

Do I need to do anything to prepare for this test?

You do not need any special preparation for a PCR test.

Is there a risk in a PCR test?

There are very few risks in taking a blood test. You may feel slight pain or bruising where the needle was placed, but most symptoms go away quickly.

A nasal swab may tickle your throat or cause you to cough. A nasopharyngeal swab can be uncomfortable and cause coughing or retching. All of these effects are temporary.

Anything else I should know about PCR testing?

PCR tests are an accurate and reliable method for identifying many infectious diseases. And because they can often make diagnoses before symptoms of infection are present, PCR tests play a crucial role in preventing the spread of disease.