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Comparing different types of testing

This article is an overview of different COVID-19 diagnostics tests
Cartoon showing a healthcare worker in lab coat and mask holding a rapid COVID-19 test facing a scientist in full PPE holding a blood tube. There is a PCR machine and reagent bottle in background with SARS-CoV-2 viral particles floating above.
© COG-Train

SARS-CoV-2 infection can be detected using different diagnostics approaches. In this article, we will cover the main tests used during the pandemic.

Lateral flow immunoassays to detect SARS-CoV-2 antigen
The swab is placed in a reagent tube, which contains a lysis buffer that disrupts the cells to expose the nucleocapsid (N) protein. When this solution, containing the specimen and reagent, is added to the testing cassette, the sample moves along a test strip. A colour change occurs when a positive sample reaches the part of the strip where the antibody against the N protein is located. The main advantages of these assays include the low cost, the speed of the assay with results obtained in less than 30 minutes, and their simplicity to perform due partly to not requiring complex equipment. However, the sensitivity and specificity depend on the brand used. Also, they are used as screening tests and RT-PCR may be needed to confirm the results.

Lateral flow immunoassays to detect SARS-CoV-2 antibody
The test principle is based on the receptor-binding domain (RBD) of the spike and nucleocapsid proteins (antigens). The cassette has dye pad sections containing Recombinant 2019-novel coronavirus nucleocapsid protein and or Recombinant 2019-novel coronavirus Spike Protein (Si Subunit). The blood/serum/plasma sample is placed in the testing cassette, the sample moves along a test strip. A colour change occurs when a positive sample (a positive sample is one containing antibodies against the SARS-COV-2 virus) reaches the part of the strip where the SARS-CoV-2 antigen is located. The advantages include the low cost, the speed of the assay with results obtained in less than 30 minutes, and it does not require complex equipment. The disadvantage is that it determines exposure but does not predict the current infection. Similarly to the above, the sensitivity and specificity depend on the brand used. The same limitations apply to other forms of antibody tests such as immunoenzymatic and chemiluminescent assays.

Reverse transcriptase real time PCR (RT-PCR)
RNA is extracted from the swab usually using a kit based method. Reverse transcriptase RT-PCR is then performed on the extracted nucleic acids. SARS-CoV-2 gene targets commonly used include the nucleocapsid, envelope protein, RNA dependent RNA polymerase, and the viral open reading frames. The Taqman, FRET and LAMP chemistries are usually used and automated and manual PCR methods are available. The advantages of this method are the high specificity and sensitivity; it is the gold standard for SARS-CoV-2 testing and therefore it serves as a confirmatory test for other assays. The disadvantages include the requirement of expensive material and equipment, that it requires expertise and training to use, presents a longer turnaround (1-4 hours), and requires a functional laboratory.

The table available for download highlights the main characteristics of the three testing platforms.

Have you ever been tested for COVID-19? What are the testing methods most commonly used in your country? Use the comments area to discuss it with your colleagues.

© COG-Train
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