FDA Authorizes a COVID-19 Diagnostic Test for Asymptomatic Individuals
Many individuals infected with SARS-CoV-2 coronavirus do not show any symptoms. Now there is a test for diagnosing COVID-19 in asymptomatic individuals.
One of the challenges in controlling the rate of new infections during the COVID-19 pandemic has been the lack of a diagnostic test specifically indicated for asymptomatic patients. According to some estimates, nearly 40% of the new cases of SARS-CoV-2 infections do not have any visible symptoms. As a result, many of those infected are not aware they are carrying the virus and may be inadvertently adding to the rising rates of new infections.
Understanding the Available Diagnostic Tests
As of this writing, the FDA has authorized 187 different tests, including 154 RT-PCR molecular diagnostic tests for COVID-19. Up until recently, none of the diagnostic tests were specifically indicated for asymptomatic individuals. FDA allowed physicians to order one of the authorized tests if they suspected COVID-19 even when the patient did not show any symptoms. Therefore, whether an asymptomatic patient got tested or not depended on a physician’s judgment.
In this blog, we are focusing on one of the RT-PCR molecular diagnostic tests, which has just been authorized to be used for “any individual, including from individuals without symptoms or other reason to suspect COVID-19”. This is an important step forward in improving broad access to diagnostic testing, which can also help generate disease surveillance data at the population or community level.
This test is from LabCorp, which originally received an Emergency Use Authorization in March, 2020. Now, it has been updated to also have be indicated for asymptomatic individuals, at home collection and pooled sampling. It targets three regions of the SARS-CoV-2 nucleocapsid (N) gene in the RNA isolated from upper and lower respiratory specimens such as nasal, nasopharyngeal or oropharyngeal swabs, sputum, lower respiratory tract aspirates, bronchoalveolar lavage and nasopharyngeal wash/aspirate or nasal aspirate. Testing is limited to laboratories designated by LabCorp that are also certified under CLIA as high complexity labs.
Here is a brief video overview of this test and validation data used to support the indication for asymptomatic individuals.
How the Test Was Authorized
20 samples, which tested positive from the Pixel screening (at home collection) where the patient self-indicated they were asymptomatic were used for validation. 113 negative samples came from an employee screening initiative. These samples were compared with 36 symptomatic positives and 57 symptomatic negatives in terms of the Ct values (Cycles threshold). On average, the asymptomatic samples had a 2 Ct shift, but they were still detectable and within the standard deviation of Ct values for symptomatic samples. An additional confirmation of these results was done using a comparator RT-PCR test which showed complete agreement of positive and negative results.
These results look good, but there are some concerns. There were only 20 samples and self-identification of lack of symptoms. Still, there is reason to believe that this specific test has performed well since its initial authorization in March, and that the risk-benefit analysis is considered favorable by the FDA to authorize an additional indication for asymptomatic individuals. The main concern with samples from asymptomatic individuals may be around sensitivity as these samples may contain a low viral load. The validation study results show that the test has sufficient sensitivity and good clinical agreement.
Why Asymptomatic Testing is Important for COVID-19
Testing asymptomatic individuals is important to ensure that those who test positive can self-isolate quickly. If they don’t know they have the virus, they may spread the virus to others. Under the current circumstances, where COVID-19 is spreading at a very high rate, the benefit of improving access to testing outweighs the risk of false negatives due to limited clinical validation data. Hopefully, additional results from real world testing will continue to increase the level of confidence in this test.
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