Team effort, flexibility needed
Dr. Mastrianni said he expected their study to find that pooled testing saved testing resources, but he “was surprised by the complexity of the logistics in the hospital, and how it really required getting everybody to work together. …There were a lot of details, and it really took a lot of teamwork.”
The nursing supervisor in the emergency department was in charge of the batch and coordinated with the laboratory, he explained. There were many moving parts to manage, including monitoring how many patients were being admitted, what their conditions were, whether they were high or low risk, and where they would house those patients as the emergency department became increasingly busy. “It’s a lot for them, but they’ve adapted really well,” Dr. Mastrianni said.
Pooling tests seems to work best for three to five patients at a time; larger batches increase the chance of having a positive test, and thus identifying the sick individual(s) becomes more challenging and expensive, Dr. Shah said.
“It’s a fine line between having a pool large enough that you save on testing supplies and testing costs but not having the pool so large that you dramatically increase your likelihood of having a positive test,” Dr. Shah said.
Hospitals will likely need to be flexible and adapt as the local positivity rate changes and supply levels vary, according to the authors.
“Pooled testing is mainly dependent on the COVID-19 positive rate in the population of interest in addition to the sensitivity of the [reverse transcriptase-polymerase chain reaction (RT-PCR)] method used for COVID-19 testing,” said Baha Abdalhamid, MD, PhD, of the department of pathology and microbiology at the University of Nebraska Medical Center in Omaha.
“Each laboratory and hospital needs to do their own validation testing because it is dependent on the positive rate of COVID-19,” added Dr. Abdalhamid, who was not involved in the current study.
It’s important for clinicians to “do a good history to find who’s high risk and who’s low risk,” Dr. Mastrianni said. Clinicians also need to remember that, although a patient may test negative initially, they may still have COVID-19, he warned. That test reflects a single point in time, and a patient could be infected and not yet be ill, so clinicians need to be alert to a change in the patient’s status.
Best for settings with low-risk individuals
“Pooled COVID-19 testing is a straightforward, cost-effective, and efficient approach,” Dr. Abdalhamid said. He and his colleagues found pooled testing could increase testing capability by 69% or more when the incidence rate of SARS-CoV-2 infection is 10% or lower.
He said the approach would be helpful in other settings “as long as the positive rate is equal to or less than 10%. Asymptomatic population or surveillance groups such as students, athletes, and military service members are [an] interesting population to test using pooling testing because we expect these populations to have low positive rates, which makes pooled testing ideal.”
Benefit outweighs risk
“There is risk of missing specimens with low concentration of the virus,” Dr. Abdalhamid cautioned. “These specimens might be missed due to the dilution factor of pooling [false-negative specimens]. We did not have a single false-negative specimen in our proof-of-concept study. In addition, there are practical approaches to deal with false-negative pooled specimens.
“The benefit definitely outweighs the risk of false-negative specimens because false-negative results rarely occur, if any. In addition, there is significant saving of time, reagents, and supplies in [a] pooled specimens approach as well as expansion of the test for higher number of patients,” Dr. Abdalhamid continued.
Dr. Mastrianni’s hospital currently has enough testing cartridges, but they are continuing to conduct pooled testing to conserve resources for the benefit of their own hospital and for the nation as a whole, he said.
The authors have disclosed no relevant financial relationships. Dr. Abdalhamid and Dr. Shah have disclosed no relevant financial relationships.
A version of this article originally appeared on Medscape.com.