SACRAMENTO COUNTY, Calif. (KTXL) — A rush for rapid COVID-19 testing kits at Sacramento County libraries last week left many without what they came for. 

Nearly half of the libraries offering the kits ran out of them on day one

The at-home test kits are the rapid antigen tests, meaning it looks for the byproduct of the pathogen in the tester’s body. 

PCR or polymerase chain reaction tests are considered more accurate because it looks for the virus’ genetic makeup and may be better at detecting the omicron variant.  

“PCR tests can detect the virus’ presence up to 48 hours prior to your symptom onset,” explained Glens Falls Hospital’s Hillary Alycon. 

Rapid tests, however, are still important for immediate results. 

“So, if you get a rapid test, a positive test at home, you know to self-isolate, you know to seek further testing to get that confirmation,” Alycon said. 

For people who want to know if they are infectious, a rapid test will provide that answer, but will only come back positive while being infectious.  

A PCR test on the other hand will detect the virus weeks after symptoms have passed.  

“If you are older, if you have risk factors, if you think you might be a candidate for some of the anti-viral drugs that are just coming available now or for monoclonal antibodies, you’ll definitely need a PCR diagnosis for that, because we’ll want to understand whether its omicron or delta all those kinds of things,” explained Dr. George Rutherford, professor of epidemiology at University of California, San Francisco.  

Another reason to get a PCR test is when a person is showing symptoms, but the rapid test comes back negative.  

“That’s when you really need to be skeptical of your results and try to seek out molecular testing, which is the PCR,” Alycon advised.  

Doctors recommend getting tested five days after exposure for people who are asymptomatic, and get tested immediately if they are experiencing symptoms.