![]() Most studies compare how good lateral flow tests are at picking up positive cases of Covid-19 against PCR testing. There is also the question of how to test the accuracy of lateral flow devices. Research from Public Health England (PHE) for example, shows that when lab scientists performed a lateral flow test they picked up 79% of cases, versus 58% of cases if the swab was performed by self-trained members of the public. This includes who performs the test, where it is done, and which brand of device is used. Other factors can also affect the accuracy of the test. They therefore may not self-isolate and could spread infection. Similarly, a test that cannot reliably identify cases could mean that people with Covid-19 are wrongly told that they have tested negative. This can cause distress, repeated testing, and in the case of Covid-19, unnecessary isolating and contacting tracing. This is important because a test may be very sensitive (pick up a lot of actual cases of a disease), but if it is not very specific it will also incorrectly pick up a lot of people who don’t have the disease. how successful it is in correctly detecting people without the condition (how many “true negatives” it detects, or the “specificity”).how successful it is in correctly detecting people with a particular condition (how many “true positives” it detects, or how “sensitive” it is),.The accuracy of a test can be measured in two main ways: How accurate are they and why do the figures keep changing? This advice has changed recently, due to changes in background levels of Covid-19 in the community, and the need to get further information about variants that are spreading. For asymptomatic testing (for example regular testing at home), a lateral flow test is suggested.Īt the time of writing, if you have a positive or inconclusive lateral flow test result, you should request a confirmatory PCR test. PCR tests are generally recommended if you are symptomatic or have had close contact with somebody who has tested positive. It is important to remember that lateral flow and PCR tests are used in slightly different ways. We have previously written about how PCR tests work before. These are tagged with a marker so that if the viral proteins are present, the test shows two stripes (one control stripe plus another which appears with a positive result).Īs we’ve said, lateral flow tests are a newer type of test for Covid-19, the other main type of test is PCR tests. If viral proteins (antigens) specific to SARS-CoV-2 (the virus that causes Covid-19) are present, they react with immune proteins on the strip called antibodies. The solution is then dropped onto the lateral flow device, where it is drawn along an absorbent strip. The swab is put into a specially formulated solution to transfer any viral material that is present. To do a lateral flow test, a sample is taken from the nose or mouth using a swab. We have previously written about lateral flow tests before. The tests work in a similar way to a pregnancy test, but measure different substances in the sample. ![]() Lateral flow tests, or lateral flow devices (LFDs), for Covid-19 are rapid tests that do not need to be processed by a laboratory. ![]() You can help us take action – and get our regular free email The Department of Health and Social Care (DHSC) has defended its use of the tests. Some experts have said that large numbers of people are being asked to unnecessarily self-isolate, based on calculations using estimates for the accuracy of the tests and the background levels of Covid-19, whilst others worry that the tests may miss a lot of cases and provide false reassurance if used inappropriately. There are also times when they can give incorrect positive results, and so if they are being very widely used, particularly in people with no symptoms, they may make some people think they are infected when they’re not.īecause of this, there has been debate around whether lateral flow tests should be used for mass screening, and whether a positive lateral flow test in this context should prompt another test by PCR to confirm the result. They are not always as sensitive as PCR tests at picking up potential cases of Covid-19, and so may give false reassurance to infected people. They can therefore be used for mass testing of people with no symptoms. They are easy to do and give fast results on the spot. Lateral flow devices are a newer type of test. Therefore, they have mainly been used in symptomatic people or people who have been exposed to a known case of Covid-19 and are already self isolating whilst they wait for the result. They can detect Covid-19 very well, but need to be processed in a laboratory. PCR tests have been the main test used for Covid-19 during the early part of the pandemic.
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