But the California Department of Public Health reports more than 57,400 people in the state still have pending test results. The longer those tests sit without diagnosis, the less likely they are to be accurate, industry experts say. That could lead to tens of thousands of people believing they've tested negative only to be asymptomatic vectors.
In a recent statement, Quest acknowledged a backlog that resulted from "a sharp influx of test orders that continued to outpace our growing capacity." It noted that for several days after it launched its test, only its lab in San Juan Capistrano, California performed SARS-CoV-2 testing, and added that much of its testing was based on its laboratory-developed test, which was "less suited to high-throughput environments."
The Secaucus, New Jersey-based lab company added it has reduced its backlog 28% since March 25, from 160,000 tests to 115,000 tests as of Wednesday.
LabCorp didn't respond to requests for comment.
"People assume that LabCorp or Quest … because they're the biggest labs, they would be the most proficient at setting up for large scale testing or molecular and they're simply not," said Rick Martin, CEO of MicroGenDx, which hopes to soon bring a product to compete against the lab giants.
Orlando, Fl.-based MicroGenDx received federal clearance for its sputum test in February. MicroGenDx then designed three primers for their laboratory-developed test, and submitted validation data to the FDA this week under the agency's emergency use authorization. Martin said that he expects approval by next week.
The firm is also seeking federal approval for the COVID-19 test even though it doesn't technically need it. Martin said MicroGenDx still wants the FDA nod because healthcare professionals often want that seal of approval.
Right now, MicroGenDx is the only commercial laboratory in the U.S. offering sputum COVID-19 testing. Other organizations, including the New England Biological Institute, are working on sputum tests for the virus, but Quest and LabCorp for the most part only accepting nasopharyngeal or oropharyngeal swabs. LabCorp has also been accepting nasopharyngeal or orpharyngeal aspirates or washes, and bronchoalveolar lavage.
Martin said his lab will soon be able to perform 14,000-15,000 tests per day. Patients might also be able to request a kit online and have it sent to their home. MicroGenDx was inspired to validate the test for sputum and saliva due to the nationwide shortage of nasopharyngeal swabs.
The sputum samples have been performing much better than the swabs, Martin said, because the viral particle load on the nasopharyngeal swabs was 3.5 million particles of SARS-CoV-2, whereas the viral load on sputum was 21 million particles. MicroGenDx's test has a limit of detection of 283 particles, according to Nick Sanford, the company's laboratory section director. The company also validated sterile saline as a transfer media, due to the low supply of viral transport media.
"If you think about it, it's logical," Sanford said. "It's an airborne droplet coming out of your nose and your mouth. The fact that anybody thinks a nasopharyngeal is required to get a diagnosis, I think is just because that's what the CDC validated first and everybody took that and ran with it."
The advantage of using sputum or saliva over a nasopharyngeal swab is the increased sample volume and the potential availability for more targets, said William Abrams, an adjunct professor at New York University's School of Dentistry. "It depends on the quantity of viral particles present in the collected sample," Abrams said. "It's likely that if the virus is actively shedding, I think are you will see it's footprint in saliva."
Part of the difficulty with sputum testing for SARS-CoV-2 is that patients with symptoms don't have productive coughs and forcing them to cough something up could spread viral particles in the air and endanger the healthcare professional taking the sample. MicroGenDx decided to try testing patients' saliva too, and noticed that saliva often had just as many, if not more, viral particles of the virus.
"If you're trying to extract RNA, if you're trying to get it out of mucus materials, it's more difficult," Martin said. "But saliva is a lot cleaner, so you're going to get a higher load of the viral RNA out of saliva than trying to get it out of the mucus material."
While MicroGenDx is the only commercial lab offering sputum-based testing for the coronavirus, several companies have developed similar sputum- or saliva-based testing for SARS-CoV-2. PerkinElmer's New Coronavirus Nucleic Acid Detection Kit, which can detect SARS-CoV-2 in sputum, plasma, or serum samples as well as oropharyngeal and nasopharyngeal swabs and bronchoalveolar lavage, received emergency use authorization from the FDA last month. Meanwhile, Primer Design, a Novacyt subsidiary, has a test that is validated for swabs and sputum as well, and Mologic is developing a saliva-based assay to detect coronavirus antigens.
MicroGenDx's test is not covered by insurance and patients will have to pay $125 out of pocket for the SARS-CoV-2 test.
This story first appeared in our sister publication, Genomeweb.