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Test for Corona (Covid-19) - How it Works?

How corona test works?
Test for Corona Virus (COVID-19)

Even after taking many precautions and implementing preventive measures, the spread of Coronavirus (COVID-19) is not showing any signs of abating. In these circumstances the entire population of the world is relying on the Corona Test performed by medical labs to identify and quarantine the affected population, thereby preventing the widespread. So let's take at how these tests are performed and how they work.

How Testing is Done?

Sample Collection

Swab Test: The lab will take a special cotton swab and sample the inside of the throat or nose of the patient. This swab is then sent to the authorized labs for testing.

Nasal Aspirate: The lab will inject a saline solution into your nose, then remove the sample with gentle suction. This sample is then sent to the authorized labs for testing.

Tracheal aspirate: A thin, lighted tube called a bronchoscope goes into your lungs, where a sample will be collected. This sample is then sent to the authorized labs for testing.

Sputum Test: Sputum is a variation of mucus from your lungs that can be coughed out or sampled from the nose with a swab. This sample/swab is then sent to the authorized labs for testing.

Blood Test: Even though not popular, collecting blood and then sent it to the authorized lab for testing is also done is some Countries.


Process of Testing

  • Once the labs receive the sample/swab, they will extract and purify the Virus RNA from the sample/swab.

  • Using reverse transcriptase enzyme complementary DNA (cDNA) is generated from the RNA.

  • The Generated cDNA is mixed with primers, where the primers are designed to only attach to characteristic parts of the cDNA. Repeatedly heating and cooling the mixture of cDNA and Primers along with DNA-building enzyme makes millions of copies of the virus cDNA.

  • The more the number of virus cDNA the more the primers that get attached to the characteristic parts of the cDNA. The fluorescent dye components added to the primers, will give off light, and based on the increase in the primer that gets attached to the virus, the light is given off will also increase. This fluorescent property is used to confirm the presence of the virus in the sample.

Positive and Negative Test Result

As already mentioned, the increase in fluorescence as more copies of virus cDNA are produced, is used to determine the presence of Virus in a Sample/Swab. If it crosses a certain threshold, then the result will be positive and Corona(COVID-19) will be confirmed in the patient. If there is no virus in the sample then, there will be no copies of the virus made, thereby no increase in fluorescence. In that case, the test will be negative.


Issues with Testing

Reagent issues: Due to the widespread of Coronavirus (COVID-19), tens of thousands of samples are sent to labs for testing every day. And to test each sample Reagents are required. This has led to a High demand and Low availability of Reagents in many countries, thereby limiting the tests performed and delaying the test speed.

Time-Consuming: It takes a lot of work and a few hours to perform one test which limits the number of tests that can be done in a day. In the situation that we are in, this can be considered a huge problem.

False Positive and Negative: In some cases, sample degeneration and contamination can result in a false positive or a false negative.

Future Test Possibilities

  • The current test is good in diagnosing the presence of the virus, but since it is a virus-based test instead of an antibody-based test, whether a patient previously has had and then recovered from the disease is impossible to determine. The Scientist and Researchers all over the world are currently working on developing such a test.

  • Tests based on virus-protein are also on the development and are considered to be faster, even though accuracy can be an issue.

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