Medical workers test nasal swab samples at a free Covid-19 coronavirus rapid antigen testing site in a car park in Bangkok. ( AFP / JACK TAYLOR)

Posts share false claim about reliability of rapid Covid tests

Copyright AFP 2017-2022. All rights reserved.

Thai-language Facebook posts shared thousands of times claim rapid antigen tests for Covid-19 are unreliable because they only detect a person's antibody levels, not their viral load. The posts shared a photo of an orange alongside a test kit showing a positive Covid result, next to a bar of soap alongside a test kit displaying a negative Covid result. But Thai health experts told AFP the image shows test kits that have been misused and said rapid antigen tests are reliable when performed correctly.

The claim was shared in this Facebook post on February 12, 2022. It has been reshared more than 6,000 times.

The Thai-language caption claims that rapid antigen tests will show two stripes for an "acidic" result -- meaning the person only has limited antibodies for Covid-19, while one stripe indicates a person has a "base" level of antibodies. 

It translates to English as: "[Rapid antigen tests] are only an antibody detection tool, they show two stripes for acidic and one stripe for base, do you want to try this?"

It continues: "Patients' bodies mostly become highly acidic when antibodies are low, the [rapid antigen test] will do its job / But it cannot determine any viruses / In summary if your secretions are acidic then everyone is infected. #ifyoustoptestingyouwontbeinfected".

The post shared a photo that shows an orange alongside a rapid antigen test kit showing a positive result, next to a bar of soap with a test kit displaying a negative Covid result.

Screenshot of the false post, taken on February 21, 2022


The same photo has been shared alongside identical claims here, here, and here.

But Thai health experts told AFP the photo shows test kits that have been misused.

Dr. Thiravat Hemachudha, the head of the Center for Emerging Infectious Diseases Health Science Center at Chulalongkorn University, said: "This is a case of misusing the antigen test kit, which shows an erroneous positive."

Dr. Kajornsak Kaewcharat, the Deputy Director-General of Thailand's Department of Disease Control said: "Antigen test kits are a reliable method to detect coronavirus when performed correctly."

AFP has previously debunked misinformation about rapid test kits being used to generate false positives, including tap water, orange juice, apple jam and cola, and beer.

Covid tests

Thailand's Department of Disease Control published this infographic outlining how to use rapid antigen tests.

It explains the tests must be carried out according to strict instructions to ensure their accuracy -- including adding the buffer fluid into the testing device before adding a sample taken from the patient's nose or throat.

Thiravat said antigen test kits can "detect protein samples of the (Covid) virus", rather than a person's antibody levels.

"Antigen tests don't detect antibody or acid/base levels," he said. "This claim is incorrect."

Kajornsak said rapid antigen tests are "useful" as an initial test for Covid-19, but those who test positive should also take an RT-PCR test to confirm their result.

"[Rapid antigen tests] are useful in screening cases within densely populated units, such as construction camps and in communities where social distancing is impossible," he said. "The results can be obtained much faster than any other testing method.

"If the test kit shows a positive result, ideally you should undergo an RT-PCR to verify the results."

The World Health Organization says rapid antigen tests can detect SARS-CoV-2, the virus that causes the disease Covid-19.