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Everything You Need To Know About Rapid Antigen Test Kits HK

5 min read

你需要進行快速抗原測試 (RAT)嗎?

The COVID-19 situation in Hong Kong is changed very rapidly with confirmed cases doubling every day, myself and the whole team at Multi Products (HK) Limited want to take this opportunity to wish every to be safe and healthy during these trying times. Protect yourself and loved with by wearing masks, washing hands frequently and avoid large groups of people as much as you can.

I’ve created this article to shed some light on the most recent events in Hong Kong, in particular are the rapid test kits for COVID-19.

Man with surgical mask holding a negative rapid test result

What is Covid Rapid Antigen Tests?

The rapid tests also known as antigen, Covid tests kits are medical devices designed to detect the SARS-CoV-2 (COVID-19) antigen. The main difference between rapid tests and the conventional ones used in hospitals and laboratories is that the rapid tests detect the infectiousness, not of infection which is why they only reliable work when there is high viral load.

Therefore, it’s very important to note:

A negative test with rapid tests is not a true indication.

Depending on when the test is taken, the viral load may not be sufficient to be detected and hence give a false false reading.

While there is no official guideline, sources online recommend to take repeated rapid test from twice in 24-48 hours to over a period of days.

Many businesses and front-line workers need to test these tests daily to ensure their safety and the people around them.

dripping liquid onto rapid test kit

How to use Rapid tests?

Depending on the test you have, you may have to do a nasal, throat or saliva swab. It’s important to read and follow the instructions on packaging carefully. If you are still unsure, or unable to read the instructions, its best to get in touch with heath care professional.

Crucially, there are 5 things you should not do 2 hours prior to the test

  • No Eating
  • No drinking (including water)
  • Don’t brush teeth/ rinse the mouth
  • No Smoking / Drinking / Alcohol
  • Don’t irrigate the nasal/nose

The environment

When you are preparing to do the test, it is most ideal to conduct it in a well-ventilated area without other people around or to maintain a 2-meter distance if this is not applicable.

If you happen to get droplets on surfaces, ensure that the area is cleaned thoroughly with 1 in 49 diluted bleach solution or 70% alcohol on metal surfaces.

women in bed coughing with hand covering her mouth

What if I am asymptomatic?

Firstly, asymptomatic means you do not show symptoms such as runny nose, high temperature, coughing etc. You can still have COVID-19 even if you are asymptomatic, furthermore, you can infect others.

If you suspect that you have been in close contact with someone who is confirmed with COVID-19, then you should follow the same guidelines as you were symptomatic such as social distance and repeat tests with the rapid antigen kit.

It’s important to note that, sources, indicate that asymptomatic people have a slightly lower sensitivity for these tests but they are still very close to high 90%.

Are you currently home quarantine or you are working from home?
Check out our blog for working from home and see how to create a more relaxed working environment.

Rapid test kit image showing positive, negative and invalid results

How do they work?

Firstly, the rapid test has an area for the specimen to be applied to called the cassette which has two lines named C and T, they stand for control and test respectively.

The control line is there to indicate that the test was successful and worked expected regardless if the result if positive or negative. If you have any result where there is no line in C, then the test is deemed invalid and another test should be taken.

If the specimen has COVID-19 antigens then it will bind to the SARS-CoV-2 antibodies coated on the (T) Test line which in turn will create a red line across the T section indicating a positive result. Together with the line in C and T, this is a positive result.

For a negative result, the line should only appear in C.

What to do if you are positive?

If both lines appear on the rapid antigen test, including if the line is faint for T, then you should immediately isolate yourself as best as possible. Stay in your room, wear a mask when you leave your room and always be vigilant of where and what you touch around the house, to prevent spreading the infection.

You should then immediately book for a nucleic acid testing for confirmation. If StayHomeSafe Scheme, please call the Home Affairs Department “StayHomeSafe Scheme”

Hotline 24-hour telephone hotline (1833 019). For more details of the StayHomeSafe Scheme please click here.

What to do if you are negative?

Please be aware that a negative test result from a rapid antigen test it not conclusive. If you have symptoms or suspect you have been with someone who has the virus, you should practice safe social distancing and repeat the test after a period of time.

What to do if the test result is invalid?

Check the procedure as listed on the packaging and ensure you followed it correctly and the repeat, if you are sure you followed the procedures correctly and still get an invalid result it could be due to faulty batch and therefore if purchasing, it would be best to get it from another location or try a different brand.

Can the rapid antigen test detect the omicron variant?

Yes, rapid antigen test kits can detect omicron, but it can less sensitive which is why its strongly suggested to not take one test, instead take several over a period of time. Furthermore, the test kits which are procured by the government also reinforce this statement that they can detect the omicron variant.

What does sensitivity mean?

The sensitivity is an indication of how accurate the test is. An example;

If 1000 people are confirmed to have the virus and use a rapid test and only 200 show negative results. That’s 200/1000 which is 20%, subtract that from 1 or 100% and you have 80% sensitivity or accuracy. You can trust the rapid test kit results 80% of the time.

However, positive rates are almost always 100% accurate.

Therefore, not matter which rapid test kit you have, it's best to take several tests.

Which rapid antigen test kit to use? 

The Consumer Watchdog has released an online tool for consumers to check if and where rapid antigen test are approved, including in US, EU and Hong Kong. The database search results will also provide clinical data, specificity and sensitivity of the test kits.

The World Health Organisation has quoted rapid antigen test should "have a minimum sensitivity of 80 percent and specificity of 97 percent” 

The link is here

man getting a nasal swab for covid test

Are there any difference between a nasal swab and throat swab?

Tests kits are usually designed for one either nasal swab or throat, not normally both, some online sources mention that omicron affects the throat more and therefore it makes more sense to check there first. On the other hand, sources indicate that saliva and cheek swab are significantly less effect with sensitivity being in the single digit.

All test kits are effective during the high viral load phase, yet a single negative result is not a true indication of being COVID free. The bottom line is to follow the instruction on your test kit and don’t improvise by choosing to swab in other locations.

rapid covid antigen test kits in shop

Should I buy and stock rapid antigen test kits?

If your job requires you to visit high risk areas or to be exposed to a large volume of people, you are more likely to be at risk to catch COVID-19 than the rest of the population. It might be wise to have some in stock or keep an eye out on the stock levels, because as soon as you have symptoms which you worry may be caused by the virus, then it would be prudent to take a rapid antigen test to protect yourself and those around you.