Understanding the Differences Between COVID Antigen and PCR Tests
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Chapter 1: Introduction to COVID Testing
In the wake of my previous series on Scientific Literacy (which I recommend checking out), I wanted to delve into the essentials of science. These concise explanations aim to clarify scientific concepts and processes, serving as a foundation for your scientific literacy. If there are specific topics you wish to explore, feel free to share in the comments. With a Ph.D. in microbiology and biochemistry, I'm equipped to investigate subjects beyond my daily focus as well.
The prior topics in the Science Fundamentals series include: DNA, PCR, Agarose Gel Electrophoresis, and Antigens/Antibodies. This particular installment discusses the distinctions between the COVID antigen test and the PCR test, contributing to an ongoing exploration of these testing methods. The earlier Science Fundamentals serve as beneficial background if any part of this article raises questions. I won’t revisit the basics of PCR here; please refer to my detailed article for that. Similarly, I'll refrain from discussing antigens/antibodies extensively, as I have already covered that topic comprehensively.
Disclaimer: I am not a medical professional. While I hold a Ph.D., my expertise lies outside of clinical practice (thanks, Disney's Treasure Planet!). Please consult a qualified healthcare provider for medical advice. My goal is purely educational, and I cannot be held liable.
Section 1.1: Key Differences Between Antigen and PCR Tests
What sets the antigen test apart from the PCR test?
Both testing methods begin with a sample collection, typically via a nasal swab using a long q-tip. The swabbing process requires reaching deep into the nasal cavity to ensure an adequate sample is obtained, which may be uncomfortable but generally poses no lasting harm.
The PCR test is considered the gold standard for detecting SARS-CoV-2, the virus responsible for COVID-19. In this method, the collected sample is sent to a laboratory where it's treated with enzymes that convert RNA into DNA. Since SARS-CoV-2 is an RNA virus, this conversion is crucial. The resulting viral DNA then serves as the template for the polymerase chain reaction (PCR), amplifying the DNA from a few fragments to millions or even billions. This amplification enables the test to accurately detect even minuscule quantities of the virus, often before symptoms manifest. The PCR test boasts an accuracy rate nearing 100%, with low incidences of false positives (when the test incorrectly indicates an infection) and false negatives (when it fails to detect an actual infection). According to a review published in 2021, PCR tests identified infected individuals correctly 95% of the time and uninfected individuals 99% of the time (Dinnes et al., 2021). However, PCR tests require skilled technicians, specialized equipment, and specific reagents, making them more time-consuming and costly.
Video Explanation: PCR vs. Antigen COVID Testing This video clarifies the distinctions between PCR and antigen COVID testing, highlighting critical aspects of both methods.
Section 1.2: Antigen Tests - A Different Approach
In contrast, the antigen test employs a different methodology. Instead of using enzymes, it utilizes a combination of soap and salts to break down any collected cells. The sample is then placed onto a test cartridge that contains synthetic antibodies designed to bind to the virus's antigens. A chemical reaction occurs if the antibodies detect the virus, resulting in a visible color change on a second strip of the test.
Antigen tests do not require highly trained personnel or costly equipment, allowing them to be administered in various settings. These tests are often referred to as rapid tests because results can be available within 10 to 15 minutes, and they tend to be more affordable. However, their accuracy is comparatively lower. The same review revealed that antigen tests detected only 72% of infected individuals displaying symptoms and dropped to 58% for those without symptoms. This limited accuracy stems from the absence of amplification; thus, the tests depend on the viral load present in the body. It is often suggested to conduct multiple antigen tests to improve detection accuracy, but this poses challenges for individuals or families needing several tests.
Video Insight: Understanding Antigen and PCR Test Differences This video provides a deeper understanding of the differences between PCR and rapid antigen tests for COVID-19.
Chapter 2: Conclusion and Further Exploration
In summary, the PCR test remains the gold standard due to its superior accuracy, while antigen tests offer a quicker and more affordable alternative but with limitations. I hope this brief overview has been informative. If you found this content helpful or have suggestions for future Science Fundamentals, please reach out. After this series, I may explore the history of science, a topic I find equally fascinating. Stay tuned for more!
Glossary
- SARS-CoV-2: The virus responsible for COVID-19.
- False Negative: A test result that incorrectly suggests the absence of a condition.
- False Positive: A test result that incorrectly indicates the presence of a condition.
Dinnes J, Deeks JJ, Berhane S, Taylor M, Adriano A, Davenport C, Dittrich S, Emperador D, Takwoingi Y, Cunningham J, Beese S, Domen J, Dretzke J, Ferrante di Ruffano L, Harris IM, Price MJ, Taylor-Phillips S, Hooft L, Leeflang MMG, McInnes MDF, Spijker R, Van den Bruel A. Rapid, point-of-care antigen and molecular-based tests for diagnosing SARS-CoV-2 infection. Cochrane Database of Systematic Reviews 2021, Issue 3. Art. No.: CD013705. DOI: 10.1002/14651858.CD013705.pub2. Accessed 09 March 2022.