COVID-19 rapid antigen tests or RATs, also frequently called COVID-19 lateral flow tests or LFTs, are rapid antigen tests used to detect SARS-CoV-2 infection (COVID-19). They are quick to implement with minimal training, cost a fraction of other forms of COVID-19 testing, and give users a result within 5–30 minutes. RATs have been used in several countries as part of mass testing or population-wide screening approaches. Many RATs can be used for self-testing, in which an individual "collects their own specimen… and interpret[s] their test result themselves".
False positives are very rare; the tests' specificity is 98%-99%. However, the tests have a sensitivity of 70%-72%, which is lower than COVID-19 polymerase chain reaction (PCR) tests' sensitivity of 88%-96%. Despite this, COVID-19 RATs remain valuable in finding people who would otherwise not know they were infected, helping to prevent further transmission. The tests are more sensitive in the symptomatic and transmissive stages of disease when the viral load is higher.
Uses
Use in diagnosis
COVID-19 rapid antigen tests (RATs) have been widely used for diagnosis of COVID-19. The World Health Organization (WHO) COVID-19 Case Definition states that a person with a positive RAT (also known as an antigen rapid diagnostic test or Antigen-RDT) can be considered a "confirmed case of SARS-CoV-2 infection" in two ways. First, the person with a positive Antigen-RDT could meet a "probable case definition" such as having recent loss of smell or taste without any known cause, or could meet certain "suspect criteria" such as having a severe acute respiratory illness. Second, the person with a positive Antigen-RDT could be asymptomatic but a "contact of a probable or confirmed case." Nevertheless, individual countries may have different case definitions of COVID-19; for example, in New Zealand a positive PCR test (not just a RAT) is necessary for a person to be considered a "confirmed case."
Use in screening
Between mid-2020 and early 2021, studies using mathematical models estimated the benefit of frequent RATs in screening populations for COVID-19. Paltiel et al studied a hypothetical college campus with 5000 students. Screening all students every two days with a "low-sensitivity, high-specificity test" (such as a RAT) would be able to control an outbreak of COVID-19. Mina et al theorized that higher-frequency screening using lower-sensitivity RATs may be more useful than lower-frequency screening using higher-sensitivity PCR tests because the former would "capture most infections while they are still infectious." The quick results of RATs would serve to limit asymptomatic spread. Larremore et al simulated various COVID-19 population screening strategies. The researchers found that "effective screening depends largely on frequency of testing and speed of reporting and is only marginally improved by high test sensitivity."
Humanitarian uses
In addition to routine community use, rapid tests have also been utilised as part of humanitarian efforts during the pandemic. Following the flooding in Jakarta in Indonesia on 2 December 2020, rapid tests were made available in flood shelters. Furthermore, following the closure of national borders in Europe following the emergence of the Alpha variant just before Christmas 2020, nearly 6,000 lorry drivers were stranded without food, effectively stopping Christmas food deliveries. Rapid tests were deployed by French firefighters within 24 hours at the Channel. Rapid tests enabled lorries to get on the road and complete their deliveries and return to their families for Christmas, demonstrating the potential global utility of having an easily implementable COVID-19 test. Médecins Sans Frontières strongly endorsed the use of rapid tests in lower- and middle-income countries, noting "COVID-19 antigen tests can deliver rapid and actionable results, ensuring timely identification of people infected with the virus at the community level".
Use for "return to normal" Spain became the first country to use rapid tests to facilitate a return-to-normal with rapid tests being widely available in pharmacies in December 2020, and a free music concert held in Barcelona for individuals who took a rapid test. A similar approach was taken in Albania to enable music festivals. However, many experts were unsure of this approach believing that "rapid tests are not the solution to restart normal life" but might be used in conjunction with other infection control techniques.