Explained: COVID-19 Home Test Kits And How They Differ From RTPCR
Home test kits that are rapid antigen kits provide test results in 15 minutes but have to be conducted repeatedly as they only identify the virus when it is active and symptomatic.
India's recent surge in COVID-19 cases has led to a severe stress on laboratories responsible for conducting and analysing the RT-PCR tests, with several of their employees also falling sick. This has resulted in the Indian Council of Medical Research to promote the use of rapid antigen tests and home-test kits for symptomatic individuals.
Even though these tests provide quick results, they come with their own share of problems of accuracy and viable data collection. These self-diagnosing kits are easily available at any pharmaceutical and give results within 15 minutes. However, the people who purchase these kits tend to not upload their results through the QR codes mentioned on the diagnostic kits.
There are also questions being raised on how accurate these tests are in comparison to the RT-PCR tests which are considered to be more reliable. BOOM spoke to Dr. Lancelot Pinto, pulmonologist, Hinduja Hospital, Mumbai, to understand the difference between the two tests and their reliability.
BOOM is also explaining the method to use home-based tests that are antigen tests to detect the virus.
What Are Home-Based Tests Kits?
Home based test kits created by companies like MyLabs, Abott are rapid antigen test kits or lateral flow tests that are available for ₹250 at pharmacies and if tested correctly, provide close to accurate results.
Explaining the accuracy, Dr. Pinto said, "Accuracy of tests are determined on their ability to detect positive results. Tests are governed by their ability to correctly test true positives (sensitivity) and true negatives (specificity). These tests help in detecting the infectivity and if a symptomatic agent is present at a given instance."
These tests are useful in surveillance, as has been pointed out by the ICMR and Health Ministry in several press conferences. However, they fail to measure any pre-symptomatic cases.
"In the first wave, with the original SARS-CoV-2 strain, both RT-PCR and RATs were helpful as most of the cases presented symptoms. It was easier to curtail the virus. The new variants are generally asymptomatic but the virus is transmissible, making it difficult for the antigen test kits to gauge the infectivity period at best," Dr. Pinto explained.
The rapid antigen tests also called as lateral flow tests can only test when the virus is active, infective, and symptomatic. If the person is pre-symptomatic, the lateral flow tests do not tend to correctly catch the virus unless some mild symptoms start developing, the pulmonologist explained.
As RT-PCR tests are taking a longer turn-around time which could lead to more people spreading the infection, the UK Government has issued an order stating that follow-up RT-PCR tests are not mandatory if a person tests positive on a lateral flow test.
Steps To Follow For Home-Based Tests
A home-based test kit contains five items: a nasal swab, a pre-filled extraction tube, a test card, an instruction manual, and a disposal bag. The user is expected to follow certain steps:
1. Download the corresponding application and scan the test card which contains details as per the ICMR requirements.
2. After filling the details, the person is expected to sanitise their hands, open the sterile nasal swab from the tail end and insert the cotton swab into each nostril.
3. On insertion, the person has to swirl the swab and then put it into the pre-filled extraction tube.
4. Once dipped, they have to fully immerse the swab into the extraction tube and then break the handle of the swab at a certain demarcated point.
5. The tube is a holder with a tiny hole that allows two drops of the sample and extraction to be dropped on the test card.
6. After dropping two drops, the person is expected to alert the application which sets a 15-minute timer for the test to be validated.
7. At the 15-minute mark, the test card shows a control line and then if the virus is present, a faint or a dark red line showing that the person is positive.
8. The user has to click a picture of the test card and upload it on the app. The app, then provides the person with their test results.
If there is no red test line below the control line, the sample is negative. If there is no control line, the test card is invalid and the person is required to test again. After using, all the items have to be put in the biohazard disposable bag provided in the packet and disposed with regular trash.
Problems With The Tests
Firstly, there are several individuals who do not follow the guidelines and do not upload their test results on the app. This suggests that many of the positive test results are going unreported. This means that the virus is prevalent among many people and the statistics that are shared by city, state, and national officials are heavily underreported.
Secondly, as Dr. Pinto mentioned, these tests are not always accurate. With a low sensitivity, they do miss out on diagnosing people who are truly suffering from the disease. According to the official health ministry guidelines, if a person who is symptomatic tests negative on the rapid tests, they are expected to undertake a standard RT-PCR test, which many of them do not follow.
Difference with RT-PCR Tests
Dr. Pinto specified that while RT-PCR tests are better at attesting who is infected, they do not really test infectivity. "As RT-PCR tests are based on amplification, they also detect dead or tiny traces of the virus which would not really be infective. While helpful, they are not necessarily testing the point at which a person infects another person."
Comparing both the tests by their accuracy, Dr. Pinto added, "In 100 people who are actually infected, the antigen tests may only correctly identify 50 patients, but the RT-PCR tests with a higher sensitivity correctly identify 70-80 patients."
In terms of waiting time for results, as RT-PCR tests revolve around extremely rigorous scientific procedures, test results take a longer time. Rapid antigen tests have a result turn-around time of 15-20 minutes. The instruction manuals of test kits mention that if results appear after 20 minutes, the test should be invalid as the test was not conducted properly.
Dr. Pinto also shared a paper published in the New England Journal of Medicine that stated that although useful, test kits did not identify when the virus was most transmissible and thus there was a need to figure out a way to detect the virus faster.
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