- According to the FDA, sample pooling allows more people to be tested quickly using fewer testing resources. It does this by allowing saliva from several people to be analyzed by just one test.
- Recently published data confirms the advantages of sample testing.
- However, if many people have the disease in the community the pooled testing could mean more headaches and work for physicians.
One method used to reduce spread of COVID-19 is lockdowns, which involve closing schools, small business, and restricting activities that bring people into close proximity, which can increase infection risk.
Another one is testing, which identifies those people who can leave quarantine because they’re negative for the virus.
If enough people can be tested, then we might be able to resume many currently restricted activities.
Such as getting our children back in school.
The problem is that we lack the capacity to PCR test (which detects the virus’s genetic material) enough of the U.S. population to be effective.
However, businesses can’t remain shut forever, and the new school year is only weeks away.
One solution, recently given emergency authorization by the Food and Drug Administration (FDA), is sample pooling PCR tests, meaning multiple samples are tested together.
What is sample pooling?
According to the FDA, sample pooling allows more people to be tested quickly using fewer testing resources. It does this by allowing saliva from several people to be analyzed by one test.
“Sample pooling has several advantages,” Jack W. Lipton, PhD, department chair and professor of translational neuroscience, College of Human Medicine at Michigan State University, told Healthline. “It allows diagnostic laboratories to increase the number of samples they can run per day.”
According to Lipton, a great deal of time is saved by combining individual samples together and “conducting a single determination for the pool,” rather than individually for each sample.
He emphasized that sample pooling can also help relieve the shortage of reagents needed to conduct these tests because, “Each pool uses the same amount of reagent that a single determination would use.”
“The FDA has advised that testing pools limited to five samples are reasonably sensitive,” Lipton continued. “However other pooling schemes and strategies are amenable to much larger samples of 10, 25, or 100.”
When need for testing is high, but infection rate is low
Data recently published in JAMA Network Open, confirms the advantages of sample testing.
“A new mathematical model we developed suggests that pool testing for COVID-19 would offer advantages over individual testing for screening groups of people where the need for tests is high but the rate of infection in the population is relatively low,” said Dr. Peter Kotanko, research director at Renal Research Institute, a division of Fresenius Medical Care North America.
Kotanko, who supervised the study, emphasized that the research team observed a low risk for false negatives and substantial cost savings.
“The strategy can be very useful in natural group settings, such as in first responders, shift workers, classrooms, hospital departments, local clusters, households, conventions and events, and long-term care facilities, to name a few,” concluded Kotanko. “As schools and businesses look to reopen in the coming months, pool testing proves to be a safe and reliable way to detect COVID-19 in those working or learning in close proximity.”
Where sample pooling works best
This type of testing only works well under certain circumstances.
“When a pool is negative, we know with reasonable confidence that everyone in that pool is negative,” said Lipton. “When a pool is positive, the lab needs to go back and rerun individual tests to determine which samples in the pool were positive.”
As the positivity increases, Lipton asserted, the usefulness of a pool decreases, as more time and materials are used analyzing the samples to find which are positive. This means pooling works best “when positivity is low.”
“Here is the caveat: Pooled testing boosts capacity if the infection levels are low because we expect most tests to come back negative,” said Stefan Thomke, PhD, professor at Harvard Business School and author of “Experimentation Works: The Surprising Power of Business Experiments,” in an emailed statement.
Thomke confirmed that when infection levels in the sample pool rise quickly, “the capacity benefit disappears as most individuals would have to be retested.”
He added that “decisions on pool size require thoughtful planning and adaptability,” so that optimal pool sizes are maintained based on not only positivity, sensitivity, and capacity but also the supply of reagents needed to conduct testing.
Limitations of sample pooling
Lipton said that sample pooling presents two challenges — sensitivity, and positivity, which could impact the tests’ accuracy.
“There is only so much room in the tiny reaction chamber where we measure for the presence of viral genetic material,” he said.
When samples are combined, only a portion of each is added, meaning “each sample in the pool is more dilute.”
So a positive sample in the pool might not give as strong a signal as if it were tested alone, increasing the risk of a false negative.
Again if many people have the disease the pooled testing could mean more headaches and work for physicians.
Lipton pointed out, as infections increase in the population, the odds that pools will be positive also increases. Possibly sending healthcare providers back to square one.
“Think about pools of 10 with a 10 percent positivity rate,” Lipton explained. “Nearly all pools would come back positive, adding extra work and time to determine who is positive in the pool, eliminating time and materials savings.”
The bottom line
Testing is necessary to reopen the economy and schools — however it’s almost impossible to do this using conventional testing methods.
The FDA has recently authorized a technique called sample pooling to significantly increase the number of people being tested.
Sample pooling is most effective in areas where infection levels are low, otherwise the time and expense of retesting may outweigh the benefits.