Covid: How reliable are rapid antigen tests?

October 2021 | Reading time: 3 minutes

New studies have discovered that rapid antigen tests are more accurate than they were previously thought to be.

As rapid antigen tests becomes more prevalent, it is only natural to be concerned about the tests’ accuracy.

When the pandemic first began, PCR tests had taken over as the go-to solution for COVID-19 detection. PCR tests are, even now, considered to be the ‘gold standard’ in terms of reliability and accuracy.

Although it is still the most trusted COVID-19 detection method, recently, the pervasiveness of PCR tests has seen some decline. With the vaccination programme’s success and social distancing rules having been called off, rapid antigen test usage has increased.

Previously, the lateral flow test (LFT), the most commonly used antigen test, garnered a reputation for presenting highly unreliable results. Recent research suggests otherwise.

Clinical study

A clinical epidemiology study found that lateral flow tests have over 80% efficacy at identifying any level of a COVID-19 infection, and they are more than 90% effective for high levels of the infection. These degrees of success are much higher than previously thought.

Prof Michael Mina from Harvard School of Public Health, as a part of the research team, said: ‘There is a spectrum of infectious amounts of the COVID-19 virus, and we show that LFTs are likely to detect cases 90-95% of the time when people are at their most infectious.

‘The tests could achieve even 100% sensitivity when viral loads are at their peak and therefore catch nearly everyone who is currently a serious risk to public health.

‘It is most likely that if someone’s LFT is negative, but their PCR is positive, then this is because they are not at peak transmissible stage.’

Find out whether you need PCR tests or Lateral Flow Tests

PCR vs Lateral flow

Prof Irene Peterson, the lead study author of the research, said, ‘Previous studies comparing the reliability of lateral flow tests and PCR tests could be potentially misleading because a PCR test is a marker of having been infected at some point within a certain window of time and does not necessarily mean someone is infectious when testing positive.’

The NHS distributes free rapid antigens tests for people without symptoms. The government advises everyone to use LFTs at least twice a week.

Read more: How to get the NHS rapid lateral flow tests?

The COVID-19 incident director at the UK Health Security Agency, Dr Sophia Makki, stated, ‘Around one in three people who have COVID-19 never show any symptoms.

‘Using LFDs (lateral flow devices) help to find asymptomatic cases who have a high viral load and are most likely to pass on the virus to others.’

Several countries around the world have also started accepting antigen tests as the pre-travel test from UK travellers. Moreover, travellers can now return to the UK from non-red list countries using antigen tests instead of PCR tests. However, under no circumstances can the free NHS tests be used for foreign travel purposes – the government has prohibited it.

Check if your travel destination accepts Rapid Antigen tests