Rapid Antigen Test Kits – Just how accurate are they?

In this post we consider just how accurate rapid antigen test kits are.

COVID-19 rapid antigen tests or RATs, also frequently called COVID-19 lateral flow tests or LFTs, are used to detect SARS-COV-2 infection (COVID-19). They are quick to implement with minimal training required and offer significant cost advantages. They cost a fraction of other forms of COVID-19 testing, such as polymerase chain reaction (PCR) tests and give users a result within 5–30 minutes.

As authorised diagnostic PCR testing facilities across the country become overwhelmed due to the Omicron variant outbreak in Australia and now New Zealand, RATs have been accepted as an effective tool for the detection of COVID 19 infection.

The therapeutic goods body known as the TGA in Australia, approved an initial number of RAT test kit manufactures for broad supply, however, since December 2021, that list has grown exponentially as the Omicron variant transmissibility increased across Australia. This growth in manufacturers seeking to provide capacity into the Australian and New Zealand markets has led to some interesting variables of quality, leading to indifferent sensitivity and specificity test results. This variability in quality can potentially lead to people receiving inaccurate results, such as false positive or false negative results.

The implication of a false positive test result can be significant by impacting business continuity and our national supply chain, especially when staff and close contacts have had to isolate due to false positive results. This is also the case when the sensitivity of RATs is poor, leading to false negative results. Although, emerging peer reviewed evidence points to specificity being of greatest concern.

The TGA in good faith are approving RAT manufacturers products based on acceptable clinical data results. The sample sizes are small and one could take the view that product is being rushed to market without being effectively peer reviewed or independently tested (using larger studies).

A cursory review of manufacturers’ instructions for use (IFU) indicates specificity levels as high as 99% in many cases and sensitivity levels of 100% in others.

Independent reviews of RAT tests are producing evidence of specificity and sensitivity levels, which are much lower than indicated in the manufacturer’s IFU. In one particular case where both the TGA and MedSafe (New Zealand) have approved a test, the specificity in one independent review was 74%, however, the manufacturer’s IFU indicates it is at 99%. Another review of multiple RAT brands demonstrates that the same RAT has a specificity of 84%.

Clearly, we do not yet have a definitive picture of the effectiveness of RATs based on manufacturers’ clinical data as shown in their IFUs, compared to independent reviews. An interpretation of the specificity level of 74% would suggest that 1 in every 4 tests conducted will produce a false positive result. This should be a point of concern as the downstream impact on people and businesses could be significant!

The key takeaway for me is that RATs have been rushed to market due to the transmissibility of Omicron, with poor levels of supporting clinical evidence for sensitivity and specificity. Therefore, caution should be exercised by federal authorities when approving future RAT supplies for broad population testing of COVID variants.

The TGA has an excellent comparative online tool for all manufacturers that have either been approved or are on the waiting list for approval.

If I was asked for a recommendation regarding which test to use, I would encourage the individual to look at brand with not just a high sensitivity rating %, but a high specificity percentage based on independent reviews.

TGA link: https://www.tga.gov.au/post-market-review-antigen-and-rapid-antigen-tests

Stay safe!