Emerging Diagnostics

Topic Overview

There are a many different types of tests for COVID-19 - rapid antigen based, nucleic acid amplification based, and antibody based. In terms of detection, the most common are variations of a nucleic acid amplification method - PCR; however, there are a few antigen based diagnostic test methods as well. Below is a video from the FDA that showcases the different types of COVID-19 tests (5).

Rapid Antigen based

Rapid Antigen Based diagnostics tests look for protein bits that makes up COVID-19 virus to see if the person has COVID or not. Antigen based tests are very specific but not as sensitive as Nucleic Acid Amplification style molecular tests. This method uses a throat / nose swab sample that can then output results in minutes. A benefit of antigen based tests is that they are cheaper and faster than PCR tests which makes this type of test useful for large groups of people. Antigen based tests are usually lateral flow assays. Below is an example of a lateral flow assay output. (1)

Nucleic Acid Amplification based

Nucleic Acid Amplification (NAA) tests functions by amplifying specific fragments of viral DNA/RNA. There are two major kinds of NAA tests: the current lab standard (RT-PCR) and newer isothermal amplification methods (LAMP, NEAR, RCA, etc...). RT-PCR runs for about 2-4 hours but may take longer due to laboratory backlogs (Kilic et al, 2020). Isothermal type methods run for a variable amount of time depending on method type but overall they are much shorter than PCR tests and are very viable for Point-Of-Care (POC) tests. NAA tests are typically test tubes. An example NAA test protocol is shown below. (2)

Keywords

Nucleic Acid Amplification (Test) - NAA(T)

A type of test that amplifies the amount of nucleic acids (DNA or RNA) so it can detect the target. The most common is PCR (Polymerase Chain Reaction).

Isothermal

Isothermal means a constant temperature. There are a few methods that are isothermal. To name a few: RCA, LAMP, RT-NEAR, RT-RPA, and NASBA.

LAMP

Loop-Mediated Isothermal Amplification

Relevant Papers

(3) Molecular and Immunological Diagnostic Tests of COVID-19: Current Status and Challenges.

The paper gives an etiology of COVID-19 and detailed explanations of various types of COVID-19 diagnostic tests. The paper is broken into sections that is easily comprehendible, it has many figures to help aid its explanation of the methods. Additionally, it compares each test as well as talk about the pros and cons of each. It is relevant because it is important to see what method is best overall - there are many factors that affect a diagnostic test's usability and the paper does a good job comparing the many methods.

(4) Nucleic Acid Amplification-Alternative Methods of Polymerase Chain Reaction (PCR).

The authors wrote a comprehensive review of the many alternative methods of nucleic acid amplification than PCR. Several methods were described: LAMP, NASBA, SDA, RCA, 3SR, and LCR. There are many graphics and figures to explain the procedure and how each of the different method types functions. The paper is separated into easily comprehendible sections - beginning with the abstract, it then gave an overview of NAA. The paper is significant because the paper describes an expansive field in just a few pages.

References

(1) - Image created BioRender.

(2) - Image created BioRender.

(3) - Kilic, T., Weissleder, R., and Lee, H. (2020). Molecular and Immunological Diagnostic Tests of COVID-19: Current Status and Challenges. IScience 23. URL https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7381402/ (Accessed 10/18/20).

(4) - Md, Fakruddin & Mannan, Shahnewaj & Chowdhury, Abhijit & Mazumdar, Reaz & Hossain, Md & Islam, Sumaiya & Chowdhury, Md. (2013). Nucleic Acid Amplification-Alternative Methods of Polymerase Chain Reaction (PCR). Journal of Pharmacy & Bioallied Sciences. Accepted. URL https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3831736/ (Accessed 11/10/20).

(5) - https://www.youtube.com/watch?v=5hu7_xIsCRg&feature=emb_title

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