Stanford Health Care can begin pooled testing for COVID-19

A Stanford Medicine test for the coronavirus has been validated for pooled testing. This method greatly increases testing capacity and conserves testing resources, which continue to be in short supply.

- By Krista Conger

Pooled testing is expected to markedly increase the COVID-19 testing capacity of the Stanford Clinical Virology Laboratory. 
Steve Fisch

Stanford Health Care can begin pooling biological samples to test for the novel coronavirus that causes COVID-19, according to guidelines issued by the Food and Drug Administration. 

Combining samples prior to testing will conserve limited resources and streamline the testing process to allow for rapid detection of COVID-19 outbreaks in schools, prisons and nursing homes. 

The technique, which has long been used to screen blood donations for the presence of HIV or hepatitis, is expected to markedly increase the testing capacity of the Stanford Clinical Virology Laboratory, which is now able to process about 4,500 tests per day. Not every sample qualifies for pool testing, however. It works best for screening populations in which most samples are expected to be negative, rather than groups with many infected people. 

“Pooled testing is most useful when routine, repeat testing is needed in congregate living areas such as skilled nursing facilities or dormitories,” said Christina Kong, MD, chief of pathology for Stanford Health Care and professor of pathology at the medical school. “It’s also likely to be helpful as people plan how best to return to work or resume school. Moving ahead with pooled testing will greatly increase our capacity to take on this kind of testing in the Bay Area to quickly identify an emerging outbreak.” 

The Stanford Clinical Virology Lab is among a handful of laboratories in the country that has submitted validation data to the FDA to begin pooling samples for coronavirus testing. Stanford Health Care was one of the first academic medical centers in the country to develop a diagnostic test for the presence of the virus that causes COVID-19, which was launched in early March. More than 126,000 tests have been performed to date.

Testing for the virus that causes COVID-19 begins with the collection of a sample from the back of the nasal cavity using specially designed swabs. After collection, the swabs are immersed in a sterile liquid for transport to a testing facility, where each individual’s sample is tested for the presence of the virus’s genetic material. A positive result indicates the person is infected with the virus.

Samples combined prior to testing

With pooled testing, samples from more than one person are combined prior to the test. A portion of each individual’s sample is included in the pool. If the pooled sample is positive for the presence of the virus, each individual sample that makes up the pool will then be tested separately to determine who in the pool is infected. 

The technique can be especially helpful for increasing testing capacity to allow screening of seemingly healthy people to detect asymptomatic but infected individuals who might fuel an outbreak. But combining samples from too many people can cause the uninfected samples to dilute an infected sample enough that the test cannot detect the virus. Stanford will begin pooling biological samples in groups of four to eight, which Kong and her colleagues have found to be an acceptable trade-off between efficiency and sensitivity for low-risk groups. 

After spending weeks validating the performance of testing pools of up to eight individuals, the researchers at the Stanford lab submitted their findings to the FDA to apply for an amendment to their existing emergency use authorization. On July 22, they learned they can begin using the technique while the FDA completes their review. 

The virology lab is now automating the pooling and record-keeping processes to further increase the efficiency of pool testing and to deliver the results as quickly as possible. 

About Stanford Medicine

Stanford Medicine is an integrated academic health system comprising the Stanford School of Medicine and adult and pediatric health care delivery systems. Together, they harness the full potential of biomedicine through collaborative research, education and clinical care for patients. For more information, please visit

2023 ISSUE 3

Exploring ways AI is applied to health care