Rapid Antigen tests are commonly used in the diagnosis of respiratory pathogens, including influenza viruses and respiratory syncytial virus (RSV). The U.S. Food and Drug Administration (FDA) has granted emergency use authorization (EUA) for antigen tests that can identify SARS-CoV-2.
This type of Covid test detects specific proteins known as "antigens" on the surface of the virus, and can identify people who are at the peak of infection, when virus levels in the body are likely to be high. Proponents argue that this could be a game changer. Antigen tests could help to keep the pandemic at bay, because they can be rolled out in vast numbers and can spot those who are at greatest risk of spreading the disease. These tests are also a key element in the testing strategies of other countries, such as India and Italy.
Antigen tests are much faster and cheaper than the gold-standard PCR Covid tests that detect viral RNA using a technique called the polymerase chain reaction (PCR). But antigen tests aren’t as sensitive as the PCR versions, which can pick up minuscule amounts of the SARS-CoV-2 virus that causes COVID-19. (For your reference, a PCR test is a type of Nucleic acid amplification (NAAT) test).
The process doesn’t require a lab, and most Rapid Antigen Covid tests provide results within 10-30 minutes, but that speed comes at the cost of sensitivity. Although these tests are reliable when an individual has a high viral load, they are far more prone to false-negative results if a person has low amounts of the virus in their body.
While antigen tests look for proteins on the surface of the virus to ascertain the presence of the pathogen, PCR (polymerase chain reaction) tests are engineered to seek genetic material called RNA that instructs the virus to make these proteins.
Both tests also require a swab from the back of your nose or throat as a sample and cannot determine whether you are contagious if positive but that’s where the similarities end.
How Accurate Are Rapid Antigen Covid Tests?
These two measures are used to determine the credibility of a test, “How well does it detect disease, and how well does it detect the absence of disease”.
Sensitivity is defined as the proportion of patients with Covid-19 who correctly get a positive result, while specificity is the proportion of patients without an infection that the test correctly identifies as negative.
In general, a highly sensitive test has a low false negative rate but runs a risk of false positives if its specificity is not up to scratch. On the other hand, a highly specific test runs a risk of false negatives if the test’s sensitivity is poor, but will generally have a low false positive rate. PCR tests are considered the gold standard because they are generally highly sensitive and highly specific.
When testing a person who has symptoms associated with COVID-19, indicating that pretest probability is high, the healthcare provider generally can interpret a positive antigen test to indicate that the person is infected with SARS-CoV-2. A negative antigen test result for a symptomatic person should be confirmed with an FDA-authorized Nucleic Acid Amplification Testing (NAAT) like a PCR Covid test.
Because of concerns about false positive results when pretest probability is low, a positive antigen test result in this circumstance should be followed by a confirmatory NAAT, recognizing that the person will be tested at a later timepoint in their illness if truly infected. Per CDC recommendations, persons who receive a positive antigen Covid test result that should undergo confirmatory PCR testing should quarantine while awaiting results of the confirmatory testing. Current recommendation is to have a confirmation test performed (the PCR test) if you still have symptoms and have had a negative rapid test.
Evaluating the results of an antigen test for SARS-CoV-2 should take into account the performance characteristics (e.g., sensitivity, specificity) and the instructions for use of the FDA-authorized assay, the prevalence of SARS-CoV-2 infection in that particular community (positivity rate over the previous 7–10 days or the rate of cases in the community), and the clinical and epidemiological context of the person who has been tested.
The sensitivity of current FDA-authorized antigen tests varies, and thus negative diagnostic testing results should be handled differently depending on the test, its stated performance characteristics, and intended application (e.g., clinical diagnosis, screening). In most cases, the manufacturers’ instructions for use of antigen tests indicate that negative test results should be considered “presumptive,” meaning that they are preliminary results.
What type of Rapid Antigen Covid Test do you use at Austin Rapid Test?
This Rapid Antigen test has an 88.4% Sensitivity and 100% Specificity, and it provides results in just 10 minutes which is the fastest emergency use authorized antigen test speed available. And unlike some clinics and drive throughs, our nurse will stay onsite until your test result is available so you get your result in 10 minutes and are not waiting hours for a clinic to send you your "rapid" results.
Which Type of Covid Test Should I Get?
As always, if you are not sure what COVID-19 test is right for you, please talk with your healthcare provider. You can also reference our information on this topic here, but conferring with your healthcare provider is still highly recommended.