Many are dusting off stockpiles from when tests were handed out for free during the pandemic – prompting fears about the validity of expired kits.

Patients are also wondering if the new escaped ‘Kraken’ mutation – the most transmissible strain yet, according to the World Health Organization – can be accurately traced with current tests.

The answer, producers say, is yes. 

How do COVID tests work?

The two most commonly used COVID tests are the lateral flow antigen test and the nucleic acid amplification test (NAAT), known in some countries as a PCR test.

Lateral flow tests look for antigens – a type of protein that sits on the surface of COVID cells. If a threshold of antigens is identified in the test’s cassette then it will show a positive line. Depending on the viral load of the patient – how many of the antigens they have – the line will show up more boldly or faintly.

Rapid flow antigen tests have been given out by the government or can be bought by individuals, who test themselves and then submit their results to public health bodies.

PCR tests collect a sample and then isolate genetic materials – not proteins – before amplifying them. This work is done when the sample is sent back to a laboratory. As the swap is amplified millions of times, this means the PCR tests is more sensitive because they are looked at in much more detail.

Can COVID tests detect variants?

Surescreen Diagnostics is a UK-based company that sent rapid antigen tests for COVID across the world, covering Europe, Australia and Latin America.

Andrew Wilcher, chief executive of the family-owned business, explained that thus far there have been “no issues” with their lateral flow tests detecting mutations. He added that the organization does “continuing surveillance”, with new clinical tests carried out as soon as a new strain is identified.

He was echoed by Penny McCormick, CEO of MyHealthChecked and Bhavika Patel who is a technical advisor on the business’ advisory board. The company distributed more than 17 million tests in the U.K. in 2022 with McCormick saying demand had been fairly consistent throughout the year.

McCormick added that so far there is no evidence of tests not working on COVID variants like Kraken. She added she believed that test providers across the globe, like her own, are continually trialing their tests on new mutations.

Will tests continue to work on future strains?

The good news is, experts believe tests will continue to work on future variants of the virus. Testing has even helped identify new strains in the past.

Patel explained: “PCR tests can help us understand the virus better because different genes are targeted which makes them more sensitive and accurate. In our tests we look for an S Gene dropout which is a key indicator to health authorities. That’s actually how the Omicron variant was identified.”

She added that data collected by labs from PCR results are fed back to national health authorities daily, with governments then choosing how best to share the findings with other countries and with the World Health Organization.

Do at home tests expire?

The simple answer is yes, and they shouldn’t be used.

Experts believe that people are using out-of-date COVID tests because they were once issued for free in some countries but no longer are. As a result, people are using the tests they have lying around instead of buying new ones.

“Expiry dates are an industry standard and are necessary if you want to get your product licensed. Usually, rapid flow tests have an expiration date of two years,” said Wilcher.

Can you use out of date tests, will they give a false positive?

The likelihood of an expired test giving a false positive is unlikely, it will be more likely to show an “invalid” result, experts say.

The main message was clear, however: don’t trust expired tests.

“The validity of the test must not be assumed. The stability data does not extend beyond the expiry date,” said McCormick.