There is a boom in DIY Covid testing – what are they and how do they work

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Bangalore: As Covid cases continue to increase exponentially across the country, epidemiologists are pushing for increased use of rapid home test kits, capable of delivering results in 15 minutes. Experts say these tests are more reliable at detecting the highly contagious Omicron variant because it multiplies rapidly inside the body during infection.

The test kit contains a swab as well as test material and a test device. Swabs are usually taken from the nose, mouth, or throat.

The device works the same as a pregnancy test kit, with two lines indicating positive results. The test can be done immediately if a person has symptoms and if exposure is suspected, the test can be done the next day.

ThePrint answers frequently asked questions about these rapid tests and the use of the kits:

What are rapid tests?

Rapid antigen tests are stick test kits that can detect the presence of live viruses in the body. Unlike RT-PCR tests which take a day to provide results, these tests can detect positive cases within 15 minutes. They work by detecting surface proteins or antigens on the living virus, usually the spike protein of the coronavirus.

Rapid tests are effective when an infected person has a high viral load or an increased amount of virus in the body. As a result, they could be ineffective during the first two days after infection.

A test kit contains a swab as well as test materials and a test device. Swabs are usually inserted over the nasopharynx (nose) or oropharyngeal (mouth or throat). Recent studies have indicated that viral loads faster peak in saliva.

The device works on lines similar to a pregnancy test kit. During sample placement, the control line first turns red to indicate that the device is not defective. A red line appears in case the test sample is positive.

As with the RT-PCR test, rapid tests also cannot detect vaccine antigens. However, unlike RT-PCR, rapid tests do not turn positive for shedding of dead virus after illness. This happens because rapid tests require an extremely high amount of virus that is only achievable by replication.


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Where are the kits available?

In India, rapid test kits can be purchased from local pharmacies and from online retailers. To date, 145 antigen-based rapid test kits have been validated (including 30 revalidations). by the Indian Council for Medical Research (ICMR). The tests approved by the United States Food and Drug Administration are also allowed in the countryside.

When to do a quick test

Rapid tests detect surface proteins on living virus when the amount of virus is high. In infected patients, this occurs between one day and four days after exposure – also the time when symptoms start to appear.

If the test is negative, it is recommended to follow up with another test after one day. If symptoms persist or exposure is strongly suspected, daily testing or RT-PCR is recommended.

If a person intends to socialize and is not sure whether they are infected, the ideal time to test would be an hour or two before meeting another person or attending a gathering.


Read also: Cough or fever first? Covid variants may cause symptoms to appear in different order, US study finds


What does a negative result mean?

Because rapid tests detect a high viral load, the tests could produce a false negative if an infection has not reached the required threshold of viral quantity.

Since the majority of India’s urban population has been vaccinated and many also have a history of Covid, the first symptoms are likely the immune response rather than those caused by the virus. In such cases, the test could produce a false negative, with the likelihood of producing a positive result after a few hours or a day later. The risks of false negatives are higher for asymptomatic infections.

What does a positive result mean?

HaveMost guidelines say that an infected person must self-isolate for 7-10 days or up to two consecutive negative tests.

Since the first results for symptomatic people might come from the immune response, a person is unlikely to become contagious until after the first symptoms.

Public health experts call for increasing the isolation period to 10 days instead of shortening it as people are likely to be infectious longer.

Most tests can also usually indicate the degree of viral load by how high they are. A a higher viral load becomes darker while a lower charge remains a lighter shade of the indicator (usually red).

(Edited by Monami Gogoi)


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