Nationally, questions have been raised about the accuracy of COVID-19 tests. North Dakota is having its own such moment after a malfunction caused the state to report 82 inconclusive tests.
Gov. Doug Burgum said 35 of the 82 tests were related to tests at long-term care facilities, and that seven were residents and 28 health care workers.
“Those 35 were all negative,” Burgum said. “They were part of the 82 false positives.”
Dr. Christie Massen said the state lab’s workers deserve credit for identifying the problem.
“This was something that would have been really hard to catch, and they are an incredibly smart team who thought something was a little bit off, so we did some checks,” she said.
It was not clear exactly what went wrong, but Massen said the re-checks caused the lab to lose confidence in 82 tests, and to recommend retesting the associated individuals.
Despite the issue, Massen retains confidence in the PCR tests the state is using, which are considered the gold standard for coronavirus diagnostics.
Their accuracy is a complex subject, however. For one thing, the test is being used under emergency authorization. That means some of the normal validation for test accuracy that would come with a commercial lab test is still under development.
The test is also affected by not just instruments and reagents in the laboratory. Its overall accuracy is also determined by the quality of the specimen itself — including when and how it was taken. The specimen’s quality can even be affected by the unique biological factors of a particular individual.
“Because PCR tests detect RNA that is specific to SARS COV 2, the specificity of the nucleic acid test for COVID-19 is very high,” Massen said. “What we do know is the manufacturers of the equipment and supplies have been leaders in the field for a long time. They are credible and reliable.”
Typically, a diagnostic test would be just one piece of the puzzle that a physician would use to arrive at a diagnosis. But, with COVID-19, the rate of asymptomatic cases is high — around 35 percent nationally, and 30 percent in North Dakota.
The high rate means doctors cannot just rely on symptoms to identify who should self-isolate or quarantine.
Asymptomatic carriers can still transmit the virus to others. Given that the disease is deadly to high-risk groups, such as those over age 65 or with an underlying health condition such as heart disease or lung disease and given that treatments are still under development to help those groups, these asymptomatic cases must also be identified and isolated as quickly as possible.
Massen said that’s why it continues to be important to follow the recommendations of the North Dakota Department of Health and the CDC.
These include staying home when sick and self-isolating if you have tested positive or quarantining if you have come in contact with an individual who has tested positive for COVID-19.
“It’s important to do this whether you’re showing symptoms or not,” she added. “Masking is also important to protect those around you. You may be mildly ill or asymptomatic. Wearing a mask will reduce the risk and the likelihood you may inadvertently pass the virus on to someone else.”
Massen said samples that come to the testing laboratory are all treated as if they are special.
“We are actually trained to treat every specimen as if it was from our parent or grandparent,” she said.
Ensuring that each and every specimen is treated with the same, high-level care helps ensure reproducibility and reliability.
Each time the North Dakota lab runs tests on a set of specimens, the run also includes a set of control specimens, Massen said.
Laboratory controls in general have known outcomes. Including at least one negative and one positive control in a given test run helps alert laboratory technicians that something went wrong with the process and that the run should be rejected.
In that case, Masson explained that the sample would generally be run again. Or, if there is insufficient testing material, the test would be returned as inconclusive and the lab would recommend the individual be retested.
“Any time we release an inconclusive result, our recommendation is to retest that individual,” Massen said.
Most commercial tests for diseases have an inherent rate for false positives and for false negatives that is part of the information that comes with the test. But this is something that’s still being discovered for COVID-19 tests, Nicole Peske, with the Department of Health told the Williston Herald.
The tests were approved under emergency authorization, and so validity testing is allowed to occur after the test is in use.
North Dakota has meanwhile reported 186 new cases of coronavirus over the Memorial Day weekend including Monday, Burgum said. The state now has 667 active, confirmed cases, 40 current hospitalizations, and 54 deaths.
More testing will be possible soon, Burgum said, as the state is standing up two new pieces of equipment, each of which can do 1,000 more tests per day.