KANE COUNTY – When it comes to COVID-19 testing, the polymerase chain reaction, or PCR, nasal swab tests were the only option during much of the pandemic. Results often took days, sometimes up to a week or longer.

But now, there are PCR tests, rapid PCR tests, saliva tests and antigen tests. So what’s the difference, and which is the best test?

Dr. Jay Liu, infectious disease physician at Northwestern Medicine Delnor Hospital in Geneva, said that the nasal PCR test continues to be the “gold standard” when it comes to COVID-19 testing.

“With a PCR test, you’re detecting DNA, which is the instruction set for the cell,” Liu explained. “A PCR tests amplify the viral DNA so it can be detected. The PCR tests are more sensitive than the antigen tests, which means they’re more likely to detect an infection. A nasal swab PCR test generally has greater than 90% sensitivity.”

On the other hand, an antigen test detects a protein carried by the virus, and all over-the-counter tests, like BinaxNow, are antigen tests, Liu said.

“Antigen tests are not as sensitive, so there are more false negatives – which means the test doesn’t pick up an infection. However, if an antigen test is positive, then you know you have [the virus], because the specificity is high,” he said. “The benefits of antigen tests are you can screen a large number of people very quickly, get results in 20 minutes and they can be less invasive. They’re cheaper and faster. The two tests use completely different technologies.”

Liu said that there are some rapid PCR tests, which can be found at some medical facilities that have the equipment. The SHIELD test, the saliva-based test developed by the University of Illinois, is a PCR test. Several school districts in Illinois, including St. Charles District 303 and Kaneland District 302, use SHIELD testing in their schools. Results for SHIELD tests usually take less than 24 hours.

However, Liu cautioned that any oral test may not be as sensitive as a test that uses a nasal swab.

“There is more likely to be more virus in the back of the nose, so the best tests are unfortunately the more painful ones,” he said. “Right now, we think saliva is less sensitive, so you’re more likely to get false negatives.”

But the bottom line? Liu said he always prefers PCR tests. But that doesn’t mean there isn’t a place for antigen tests, he said.

“Antigen tests are good for mass screenings, when you need to screen a lot of people at once and get a quick answer,” he said. “Also, if you need to know immediately, get rapid PCR test — which requires a special machine, and some clinics and urgent cares have it. But if you can wait a day or two, get the standard PCR test.”

Where can you get tested for COVID-19 in Kane County?

The Illinois Department of Public Health operates a free, community testing site at 2450 N. Farnsworth Ave., across from the Chicago Premium Outlets in Aurora. The drive-thru and walk-up testing site is open Monday, Wednesday, Friday and Saturday from 8 a.m. to 4 p.m. Testing is free and available to all regardless of age, COVID-19 symptoms, or insurance status. A parent or guardian must be present and able to provide consent for individuals under age 18. Individuals being tested at the Aurora site will receive a call from 1-888-297-7208 within four and seven calendar days with test results.

CVS Pharmacy – Appointments are required. Locations include 1500 Lincoln Hwy., St. Charles, and 255 McLean Blvd., South Elgin. Hours: 9 a.m. - 6 p.m. Mon- Sat., 10 a.m.- 6 p.m. Sunday.

Physicians Immediate Care – 2490 Bushwood Dr., Elgin and 2853 Kirk Road, Aurora. Hours: 8 a.m. - 4:30 p.m. Monday through Friday; 8 a.m. - 2 p.m. Saturday and Sunday. Curbside exam may be required to determine if testing is appropriate and capacity may be limited.

VNA Health Center – By appointment at 400 N. Highland Ave., Aurora. Hours: Mon. - Sat.: 8:30 a.m. - 2:30 p.m., 1400 Indian Ave., Aurora. Hours: Mon. - Fri.: 8:30 a.m. - 2:30 p.m., 800 Villa St., Elgin. Hours: Mon. - Sat.: 8:30 a.m. - 2:30 p.m., 620 Wing St., Elgin. Hours: Mon. - Fri.: 8:30 a.m. - 2:30 p.m.

Walgreen’s Pharmacy – Appointments are required. 2100 W. State St., Geneva, 3351 W. Main St., St. Charles, 1918 W. Fabyan Parkway, Batavia. Walgreen’s offers the standard PCR nasal swab tests, and select locations have rapid tests. Testing is done through a drive-thru, contact-less process where patients self-swab.

Northwestern Medicine Delnor Hospital in Geneva requires a Northwestern Medicine physician order for testing.

The Kane County Health Department does not offer COVID-19 testing, nor does it provide test results.

A comprehensive list of testing sites across Illinois is available on the Illinois Department of Public Health website.