(CNN)While commercial labs across the country have pushed hard this year to scale up their coronavirus testing capacity, the number of tests they conduct each week has fallen over the last month.
Some of those major labs now report unused capacity, and one of the largest diagnostic companies has recently only been using about half of its total testing capabilities.
Though the dip in testing overlaps with an overall decrease in the rate of new coronavirus cases, some public health experts continue to say the US should do more testing to effectively trace the virus' spread.
Quest Diagnostics' figures show the company performed an average of about 86,000 tests per day over the last week, though its labs now have capacity to conduct about 165,000 tests per day.
"We continue to intend to scale up our capacity to 185,000 tests a day by Labor Day with further gains possible after that," Quest said in a statement.
LabCorp can run 200,000 tests per day but the company said in a statement that "volumes received are currently below that number."
Data from the American Clinical Laboratory Association, whose members include LabCorp, Quest and other commercial labs, show that weekly tests performed by ACLA labs have dropped from about 2.8 million the week ending July 26 to about 2.1 million the week ending August 23 -- about a 25% decrease.
ACLA labs on Monday performed about 180,000 tests, the lowest number since early June.
ACLA President Julie Khani said in a statement that demand for testing fluctuates but labs across the country are still developing new tests and methods "to make sure that our capacity can be utilized where it is most needed."
'A dramatic decrease'
The decline among commercial labs' testing in part reflects downward trends in national coronavirus testing. The average of new tests was about 706,000 for each day in August, whereas the daily average was about 744,000 in July, according to data from the COVID Tracking Project.
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Some public health experts describe the trend as alarming.
"You've got a clear need for more testing and yet a dramatic decrease," said Dr. Jonathan Quick, who directs the pandemic response for the Rockefeller Foundation, which has said the US should expand capacity to be able to perform 30 million tests per week by October.
Quick said that a decrease could in part be driven by some people deciding not to get tested due to long wait times for results in preceding weeks, among other factors, but he added, "I see the pattern and some of it from a public health point of view just doesn't make any sense."
Dr. William Morice, president of Mayo Clinic Laboratories, said that while his company's labs have most days been running at close to capacity, he believes there are multiple causes for the national dip in testing.
He cited the decline in the daily rate of new infections this month as one reason. "Clearly, when there is a drop in cases, there is going to be a drop in demand for testing," Morice said.
He also said changes in the rates of infection can have exponential effects on testing.
"As the community rate of infection starts to go down, not only do the number of people who are symptomatic and therefore need testing go down, but the number of their contacts that need testing goes down as well."
Change in guidelines
The unused testing capacity at some labs comes as the US Centers for Disease Control and Prevention has changed its Covid-19 testing guidelines. The agency no longer recommends testing for some people without symptoms, even if they've been in close contact with an infected person.
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Although a reduction in testing could result in fewer infections detected, Dr. Ferric Fang, a University of Washington professor of laboratory medicine, said that a national decline in hospitalizations indicates that the number of new infections is truly falling.
He attributes this to the effectiveness of social distancing, mask wearing and other preventative measures in states with recent surges.
"With fewer people presenting with symptoms suggestive of infection, there will be a reduced demand for testing and fewer tests performed. That is a good thing," Fang said.
But David Grenache, president of the American Association for Clinical Chemistry, described the decline in testing as "unusual and inconsistent" across the country.
He called that decline, "concerning given the importance of testing during a pandemic."
