Most of us have been tested for COVID-19 over the past few years. If that’s true of you, you know the routine: you go to a testing site, give your sample, a medical professional sends it to a laboratory, and you receive your results in a day or two. If this sounds familiar, you’ve benefited from PCR (Polymerase Chain Reaction) testing.
PCR is well known for its accuracy. It has limitations, however: it’s costly, time-consuming, and requires samples to be sent to central laboratories. These are drawbacks for providers who want to provide quick, inexpensive diagnoses at the point of care (POC).
Researchers are currently working on ways to resolve these issues while preserving PCR’s accuracy, and while they are making progress, overcoming all three issues at once has proved challenging.
What is PCR?
PCR is a laboratory technique for rapidly producing between millions and billions of copies of a specific segment of DNA. Developed in 1983 by biochemist Dr. Kary B. Mullis, PCR uses cycles of heating and cooling to denature (or untangle) double-strand DNA into a single strand, anneal primers, and elongate DNA. This process amplifies the DNA so it can be studied in greater detail.
By targeting particular DNA, PCR is able to identify fragments of genetic material to help users decide on identification or diagnosis.
PCR has changed over the years. Since its development in 1983, there have been three generations of PCR:
- Endpoint PCR: Also called ordinary PCR, endpoint PCR refers to the original technology developed by Dr. Mullis. Endpoint PCR uses the PCR thermal cycler to amplify DNA and other detection methods to find the target DNA. This type of PCR can only provide a qualitative result to determine if specific genetic material is present.
- Quantitative PCR: Quantitative PCR (qPCR) is also called real-time PCR. By using dye and a probe, qPCR allows researchers to monitor the amplification process in real-time. This method is able to tell research how much genetic material is in a sample. This type of PCR is usually referred to as the gold standard of infectious disease testing.
- Digital PCR: The most recent generation of PCR is able to precisely identify how much of a viral load a patient is carrying. Digital PCR (dPCR) divides a sample into microscopic units and performs the denaturing, annealing, and elongation on each unit individually. Using this information, researchers can build a precise picture of how much genetic material is in a sample.
What is the difference between PCR and antigen testing?
PCR testing is just one of the testing methods used to diagnose COVID-19 cases. Rapid Antigen Testing — known to patients as the self-administered test kits that allowed them to test for the virus at home — is also widely used.
Antigen testing uses a synthetic antibody to detect a protein on the outside of the virus. If the virus is present in a patient, the antibody attaches to the virus, which generates a positive result.
There is a lot to be said for antigen tests; they’re fast, generating results in 15 minutes. They’re inexpensive, and patients can take them without going to a medical facility. However, there’s a trade-off; antigen tests are not very accurate.
While PCR tests are sensitive enough to pick up COVID in patients with no symptoms and a low viral load, antigen tests only work well if there is a lot of virus in a patient’s system. For this reason, antigen tests are only recommended if a patient is already showing symptoms.
A look at the evolution of PCR
The accuracy of PCR has made it the gold standard of infectious disease testing, but its accuracy comes with limitations. At the height of the pandemic, for example, the sheer volume of testing meant that labs were overtaxed, samples were bottlenecked and there was a shortage of supplies.
To avoid similar situations, the market needs better PCR technologies. Medical providers can’t provide fast PCR results at the point of care, for example. PCR technology also needs to be simpler and less expensive.
Recently, researchers have been making headway on some of these challenges.
Faster PCR
The most time-consuming part of the PCR process is thermal cycling; samples are subjected to between 30 and 50 cycles of temperature intervals. Researchers are exploring several methods of shortening this process, such as changing the shape of the reaction well, changing the composition of the thermal block, using a new heating mechanism such as a resistive heater, and more directly applying energy for thermal cycling to the samples (such as with a laser or LED lights). The key here is to realize fast and precise temperature control.
Making PCR simpler
PCR requires multiple steps of handling from sample preparation to read-out. To encourage wider adoption of PCR, the industry has tried to automate the process. A high-throughput workstation was developed for the central laboratories by adding robotics into the PCR workflow, for example. For point-of-care testing, miniaturized integrated systems using disease-specific cartridges incorporating microfluidics technology have been developed.
Can PCR be made less expensive?
Cheaper PCR that does not compromise accuracy, speed, or usability is the holy grail of clinical diagnostics. Unfortunately, as of now, there’s no simple answer to this problem. Most companies try to reduce the cost of PCR by cutting costs in business areas, such as manufacturing or supply chain management.
That’s not sustainable, however. The best way of achieving cost competitiveness in PCR is that the core technology that enables both speed and ease of use should also contribute to its cost-effectiveness. This is why it is so challenging to make a truly innovative PCR system.
What does the future of PCR hold?
PCR is constantly evolving and is likely to look different in the future than it does today. For example, the miniaturization of PCR means that diagnostic testing and forensic work may be done in the field, using portable devices and smartphones, rather than in a lab.
Future PCR testing can identify specific variations of disease, or test for more than one condition at a time. It may replace other longstanding methods of diagnosis, such as culture-based testing.
PCR may be an old technique, but it has developed over the years, and we expect it will play as a gold standard in diagnostic medicine for decades to come.
About Jinyong Lee
Jinyong Lee is the CEO and Co-Founder of Kryptos Biotechnologies whose technology called photothermal heating – uses light to generate and control heat for fast and accurate Polymerase Chain Reaction to build an integrated sample-to-answer molecular diagnostics system for point-of-care testing. Lee oversees the company’s overall business including financing, strategic planning, business development, and investor relations.
Prior to Kryptos, Lee served clients in various industries including Technology, Private Equity, Finance, Consumer products, Chemicals, Construction, and Heavy industries sectors.
