PCR

What is PCR?

Polymerase chain reaction (PCR) is a common laboratory technique used in research and clinical practices to amplify, or copy, small segments of genetic material. PCR is sometimes called “molecular photocopying,” and it is incredibly accurate and sensitive. Short sequences called primers are used to selectively amplify a specific DNA sequence. PCR was invented in the 1980s and is now used in a variety of ways, including DNA fingerprinting, diagnosing genetic disorders and detecting bacteria or viruses. Because molecular and genetic analyses require significant amounts of a DNA sample, it is nearly impossible for researchers to study isolated pieces of genetic material without PCR amplification.

How does COVID-19 PCR testing work?

COVID-19 testing uses a modified version of PCR called quantitative polymerase chain reaction (qPCR). This method adds fluorescent dyes to the PCR process to measure the amount of genetic material in a sample. In this instance, healthcare workers measure the amount of genetic material from SARS-CoV-2.

PCR

The testing process begins when samples are collected using a nasal swab, saliva tube or stool vial. The SARS-CoV-2 virus, which is the pathogen that causes COVID-19, uses RNA as its genetic material. First, the PCR is converted from single-stranded RNA to double-stranded DNA in a process called reverse transcription. The two DNA template strands are then separated.

PCR

Primers attach to the end of these strands. Primers are small pieces of DNA designed to only connect to a genetic sequence that is specific to the viral DNA, ensuring only viral DNA can be duplicated (right). After the primers attach, new complementary strands of DNA extend along the template strand. As this occurs, fluorescent dyes attach to the DNA, providing a marker of successful duplication. At the end of the process, two identical copies of viral DNA are created. The cycle is then repeated 20-30 times to create hundreds of DNA copies corresponding to the SARS-CoV-2 viral RNA.

What do results mean for a COVID-19 PCR test?

 

A positive result happens when the SARS-CoV-2 primers match the DNA in the sample and the sequence is amplified, creating millions of copies. This means the sample is from an infected individual. The primers only amplify genetic material from the virus, so it is unlikely a sample will be positive if viral RNA is not present. If it does, it is called a false positive.

negative result happens when the SARS-CoV-2 primers do not match the genetic material in the sample and there is no amplification. This means the sample did not contain any virus.

false negative result happens when a person is infected, but there is not enough viral genetic material in the sample for the PCR test to detect it. This can happen early after a person is exposed. 

PCR

Antibody Testing

antibody covid PCR and Antibody TestsCOVID-19 antibody testing, also known as serology testing, is a blood test that’s done to find out if you’ve had a past infection with SARS-CoV-2, the virus that causes coronavirus disease 2019 (COVID-19). An antibody test can’t determine whether you’re currently infected with the COVID-19 virus.

Antibodies are proteins produced by your immune system in response to an infection. Your immune system — which involves a complex network of cells, organs and tissues — identifies foreign substances in your body and helps fight infections and diseases. After infection with the COVID-19 virus, it can take two to three weeks to develop enough antibodies to be detected in an antibody test, so it’s important that you’re not tested too soon.

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