What do we know about false positives with rapid antigen testing?
What do we know about false positives with rapid antigen testing?
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Antigen tests for COVID-19 have many advantages, including rapid results, cheap production costs, and a high rate of accurate test results for people who are actively infected with COVID-19. However, one of the major downsides of these tests is their high rate of false negative results (having a negative test result even if you are actively infected with the virus). Comparatively, false positive test results, which incorrectly show that a healthy person is infected by the virus when they are not, are very rare in tests that have been approved by regulatory agencies like the U.S. Food and Drug Administration (FDA). Despite having low rates of false positives, these types or errors in antigen tests still exist due to technical issues like handling, contamination, or test errors. These considerations have a large impact as their effects can directly result in health impacts for people who test positive (but are not) and are quarantined with people with active infections or receive treatments like medication when it may be harmful. While most newer antigen tests aim to accurately identify people with active COVID-19 infections at least 80% and 90% of the time (true positive rate), some antigen tests have been reported to have false positive or false negative rates as high as 50%. Several experts recommend using a second test to confirm a patient is truly negative or positive, particularly when patients may have no symptoms or have not been exposed to people who tested positive for the virus. While antigen tests can usually diagnose active COVID-19 infections, they are more likely to miss an active infection in comparison to molecular tests like polymerase chain reaction (PCR) tests. Several countries have begun authorizing the use of newer antigen tests that report lower rates of false positives and false negatives. For example, as of early December 2020, the U.S. FDA has granted Emergency Use Authorizations (EUAs) for a handful of the more accurate antigen tests that are available. As more of these tests are produced and used on a wide scale, we hope to learn more about their accuracy and achieve as sensitive (correctly identifying those who are are actively infected with the virus) and specific (correctly identifying those who do not have an active infection) as possible.
Antigen tests for COVID-19 have many advantages, including rapid results, cheap production costs, and a high rate of accurate test results for people who are actively infected with COVID-19. However, one of the major downsides of these tests is their high rate of false negative results (having a negative test result even if you are actively infected with the virus). Comparatively, false positive test results, which incorrectly show that a healthy person is infected by the virus when they are not, are very rare in tests that have been approved by regulatory agencies like the U.S. Food and Drug Administration (FDA). Despite having low rates of false positives, these types or errors in antigen tests still exist due to technical issues like handling, contamination, or test errors. These considerations have a large impact as their effects can directly result in health impacts for people who test positive (but are not) and are quarantined with people with active infections or receive treatments like medication when it may be harmful. While most newer antigen tests aim to accurately identify people with active COVID-19 infections at least 80% and 90% of the time (true positive rate), some antigen tests have been reported to have false positive or false negative rates as high as 50%. Several experts recommend using a second test to confirm a patient is truly negative or positive, particularly when patients may have no symptoms or have not been exposed to people who tested positive for the virus. While antigen tests can usually diagnose active COVID-19 infections, they are more likely to miss an active infection in comparison to molecular tests like polymerase chain reaction (PCR) tests. Several countries have begun authorizing the use of newer antigen tests that report lower rates of false positives and false negatives. For example, as of early December 2020, the U.S. FDA has granted Emergency Use Authorizations (EUAs) for a handful of the more accurate antigen tests that are available. As more of these tests are produced and used on a wide scale, we hope to learn more about their accuracy and achieve as sensitive (correctly identifying those who are are actively infected with the virus) and specific (correctly identifying those who do not have an active infection) as possible.
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What our experts say
Antigen tests for COVID-19 have many advantages, including rapid results, cheap production costs, and a high rate of accurate test results for people who are actively infected with COVID-19. However, one of the major downsides of these tests is their high rate of false negative results (having a negative test result even if you are actively infected with the virus). Comparatively, false positive test results, which incorrectly show that a healthy person is infected by the virus when they are not, are very rare in tests that have been approved by regulatory agencies like the U.S. Food and Drug Administration (FDA).
Despite having low rates of false positives, these types or errors in antigen tests still exist due to technical issues like handling, contamination, or test errors. These considerations have a large impact as their effects can directly result in health impacts for people who test positive (but are not) and are quarantined with people with active infections or receive treatments like medication when it may be harmful.
While most newer antigen tests aim to accurately identify people with active COVID-19 infections at least 80% and 90% of the time (true positive rate), some antigen tests have been reported to have false positive or false negative rates as high as 50%.
Several experts recommend using a second test to confirm a patient is truly negative or positive, particularly when patients may have no symptoms or have not been exposed to people who tested positive for the virus. While antigen tests can usually diagnose active COVID-19 infections, they are more likely to miss an active infection in comparison to molecular tests like polymerase chain reaction (PCR) tests.
Several countries have begun authorizing the use of newer antigen tests that report lower rates of false positives and false negatives. For example, as of early December 2020, the U.S. FDA has granted Emergency Use Authorizations (EUAs) for a handful of the more accurate antigen tests that are available. As more of these tests are produced and used on a wide scale, we hope to learn more about their accuracy and achieve as sensitive (correctly identifying those who are are actively infected with the virus) and specific (correctly identifying those who do not have an active infection) as possible.
Antigen tests for COVID-19 have many advantages, including rapid results, cheap production costs, and a high rate of accurate test results for people who are actively infected with COVID-19. However, one of the major downsides of these tests is their high rate of false negative results (having a negative test result even if you are actively infected with the virus). Comparatively, false positive test results, which incorrectly show that a healthy person is infected by the virus when they are not, are very rare in tests that have been approved by regulatory agencies like the U.S. Food and Drug Administration (FDA).
Despite having low rates of false positives, these types or errors in antigen tests still exist due to technical issues like handling, contamination, or test errors. These considerations have a large impact as their effects can directly result in health impacts for people who test positive (but are not) and are quarantined with people with active infections or receive treatments like medication when it may be harmful.
While most newer antigen tests aim to accurately identify people with active COVID-19 infections at least 80% and 90% of the time (true positive rate), some antigen tests have been reported to have false positive or false negative rates as high as 50%.
Several experts recommend using a second test to confirm a patient is truly negative or positive, particularly when patients may have no symptoms or have not been exposed to people who tested positive for the virus. While antigen tests can usually diagnose active COVID-19 infections, they are more likely to miss an active infection in comparison to molecular tests like polymerase chain reaction (PCR) tests.
Several countries have begun authorizing the use of newer antigen tests that report lower rates of false positives and false negatives. For example, as of early December 2020, the U.S. FDA has granted Emergency Use Authorizations (EUAs) for a handful of the more accurate antigen tests that are available. As more of these tests are produced and used on a wide scale, we hope to learn more about their accuracy and achieve as sensitive (correctly identifying those who are are actively infected with the virus) and specific (correctly identifying those who do not have an active infection) as possible.
Context and background
Generally, concerns about antigen tests are usually around its rate of false negatives, but recent outbreaks and articles have concerned many in public health and medicine about rates of false positive and false negative results. While newer tests have aimed to positively identify active cases of COVID-19 in at least 80-90% of cases, and preferably higher, there is wide variance between antigen tests currently available on the market and the accuracy depends on the context of use. For example, the New York Times reported that Quidel’s antigen test by the University of Arizona detected only 32% of infections in asymptomatic individuals, despite the test meeting the U.S. FDA's requirements for EUA approval.
On November 3, 2020, the U.S. FDA released a warning letter that reminds clinical laboratory staff and healthcare providers of the risks of false positive and false negative results with antigen tests, particularly when users do not follow instructions and read test results before or after the specified time. Additionally, the rate of false positives is higher when the prevalence of disease is low in a population.
On December 5, 2020, the U.S. Centers for Disease Control and Prevention (CDC) released updated interim guidance for antigen testing, including the deletion of the word "rapid" because the FDA has authorized laboratory-based antigen testing. According to the U.S. CDC guidance, the "gold standard" for COVID-19 clinical diagnosis is still nucleic acid amplification tests (NAATs), such as PCR tests.
With different COVID-19 tests remaining in circulation longer and more accurate antigen tests entering the market, our readings of the virus should become more accurate over time.
Generally, concerns about antigen tests are usually around its rate of false negatives, but recent outbreaks and articles have concerned many in public health and medicine about rates of false positive and false negative results. While newer tests have aimed to positively identify active cases of COVID-19 in at least 80-90% of cases, and preferably higher, there is wide variance between antigen tests currently available on the market and the accuracy depends on the context of use. For example, the New York Times reported that Quidel’s antigen test by the University of Arizona detected only 32% of infections in asymptomatic individuals, despite the test meeting the U.S. FDA's requirements for EUA approval.
On November 3, 2020, the U.S. FDA released a warning letter that reminds clinical laboratory staff and healthcare providers of the risks of false positive and false negative results with antigen tests, particularly when users do not follow instructions and read test results before or after the specified time. Additionally, the rate of false positives is higher when the prevalence of disease is low in a population.
On December 5, 2020, the U.S. Centers for Disease Control and Prevention (CDC) released updated interim guidance for antigen testing, including the deletion of the word "rapid" because the FDA has authorized laboratory-based antigen testing. According to the U.S. CDC guidance, the "gold standard" for COVID-19 clinical diagnosis is still nucleic acid amplification tests (NAATs), such as PCR tests.
With different COVID-19 tests remaining in circulation longer and more accurate antigen tests entering the market, our readings of the virus should become more accurate over time.
Resources
- Which test is best for COVID-19? (HMS)
- Coronavirus antigen tests: quick and cheap, but too often wrong? (Science)
- Why False Positives Merit Concern, Too (NYT)
- Why Trump’s Rapid-Testing Plan Worries Scientists (Atlantic)
- Coronavirus: India tries new type of tests to tackle virus (BBC)
- India's new paper Covid-19 test could be a ‘game changer’ (BBC)
- Countries turn to rapid antigen tests to contain second wave of COVID-19 (Reuters)
- Rapid tests. PCR. Antigen. Antibody. These are coronavirus test options, and what’s coming (SFC)
- Current Molecular and Antigen Tests with FDA EUA Status (John Hopkins University)
- A Rapid Virus Test Falters in People Without Symptoms, Study Finds (NYT)
- Potential for False Positive Results with Antigen Tests for Rapid Detection of SARS-CoV-2 - Letter to Clinical Laboratory Staff and Health Care Providers (U.S. FDA)
- Interim Guidance for Antigen Testing for SARS-CoV-2 (U.S. CDC)
- Which test is best for COVID-19? (HMS)
- Coronavirus antigen tests: quick and cheap, but too often wrong? (Science)
- Why False Positives Merit Concern, Too (NYT)
- Why Trump’s Rapid-Testing Plan Worries Scientists (Atlantic)
- Coronavirus: India tries new type of tests to tackle virus (BBC)
- India's new paper Covid-19 test could be a ‘game changer’ (BBC)
- Countries turn to rapid antigen tests to contain second wave of COVID-19 (Reuters)
- Rapid tests. PCR. Antigen. Antibody. These are coronavirus test options, and what’s coming (SFC)
- Current Molecular and Antigen Tests with FDA EUA Status (John Hopkins University)
- A Rapid Virus Test Falters in People Without Symptoms, Study Finds (NYT)
- Potential for False Positive Results with Antigen Tests for Rapid Detection of SARS-CoV-2 - Letter to Clinical Laboratory Staff and Health Care Providers (U.S. FDA)
- Interim Guidance for Antigen Testing for SARS-CoV-2 (U.S. CDC)
