By Alexander Tin, CBS News
COVID-19 tests are in greater demand than ever, and new data about the Omicron variant can make picking and using different types of tests confusing. Molecular tests for COVID-19, like the "RT-PCR" technology used by many laboratories — known as PCR tests — are widely considered the "gold standard" for spotting the most infections caused by SARS-CoV-2.
By comparison, "antigen" or "lateral flow" tests, which can be done at home and return faster results, are less sensitive than PCR tests, but could be useful for identifying cases when people are likely to be contagious. One review last year estimated rapid antigen tests might only detect on average 75% of cases that PCR tests can spot, with antigen tests performing best in symptomatic people within the first week of their disease.
Some public health officials have advocated for wider adoption of antigen testing by Americans — if they can manage to find one of the rapid at-home tests — as an added layer of protection that might spot more cases before they spread.
But many factors can affect how likely a COVID-19 test is to accurately spot an infection. Here's the latest on how these two types of tests work and why they might sometimes offer different results:
A refresher: How PCR and antigen tests work
Most laboratories generate their COVID-19 test results through a molecular testing process called reverse polymerase chain reaction, or RT-PCR, that has been used for years to diagnose a variety of diseases.
A patient gets tested with a nasal or throat swab, or in some cases provides a saliva sample. Then, using chemicals and specialized equipment, scientists mix the sample collected from the patient with the ingredients needed to create copies of the genetic material that makes up the virus. By repeating many cycles of this process, special sets of primer and probe chemicals can be targeted by test manufacturers to look for distinctive signs of SARS-CoV-2 — the virus that causes COVID-19.
"The PCR test, it's looking for that genetic material inside the virus and you don't have to have a huge viral load to pick up for it to be sensitive and specific, meaning it functions extremely well under a variety of circumstances to include the asymptomatic as well as the symptomatic," said Dr. Emily Volk, president of the College of American Pathologists.
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