A person at a new saliva testing center for COVID-19 in the Minneapolis Convention Center dropped a saliva sample into a collection box. (Star Tribune/The Minnesota Star Tribune)

Minnesotans have an array of options to get tested for COVID-19, including hundreds of sites run by hospital systems and other private providers, and a network of sites run by the state Health Department that offer free testing and may accommodate walk-ups.

Q: What kinds of tests are available to detect COVID-19?

A: Doctors say there are two main types of tests for diagnosing an active COVID infection that are most relevant to the general public in Minnesota today: nasal-swab testing and saliva testing.

Nasal-swab testing is the type done by most private health care providers and involves having a long, flexible swab inserted into the nose and swirled around for a minute or less.

Saliva testing is conducted at the state's testing sites or at home, and requires the person being tested to spit for about 10 minutes into a plastic tube. This is a good way to find cases that never show symptoms, which the CDC says comprise as many as 40% of COVID cases. Testing is open to any Minnesota resident and an appointment is recommended. Some state testing sites also offer nasal-swab testing.

Q: How accurate are those tests?

A: Standard nasal swab and saliva tests process samples in a PCR (polymerase chain reaction) machine in a lab, which is considered the gold-standard method of diagnosing a COVID-19 infection.

But timing is important. A PCR test may miss an active case if the test is given too early in the viral incubation period. One recent study found PCR testing correctly detected positive cases most reliably eight days after transmission; if the case is symptomatic, that would often be three days after symptoms appear.

Q: With nasal and saliva testing, it typically takes 24 to 72 hours to get results back. Are there faster tests?

A: Yes, there are COVID-19 tests on the market that can deliver results in hours, not days.

They react to molecular traces of the virus' genetics, and include Abbott Laboratories' point-of-care ID Now test and Hologic's lab-based Panther Fusion test for COVID.

Capacity at the private clinics for rapid tests is limited, however, so getting an appointment for one can be difficult.

Q: What's this antigen testing I keep hearing about?

A: Antigens are viral proteins that can be detected in a nasal swab. Several companies offer point-of-care antigen tests, which means results are typically available within 15 minutes, before the appointment is over.

Antigen testing for COVID-19 is being done at many nursing homes and in some schools. It can detect cases earlier in the disease course than PCR can.

A positive detection of antigens is considered very accurate, but antigen tests miss more positives than PCR testing. That's why a negative antigen test may need to be confirmed later with a negative PCR test in Minnesota.

Q: What about antibody testing?

A: As of today, antibody tests are only used in individuals to detect past infections, not active cases, using a blood sample. They peak in effectiveness weeks after the onset of symptoms. Antibody tests may be used in studies of community spread of the virus, and to find donors whose antibody-rich plasma may help other COVID patients fight the virus.

Antibody tests are not offered at state testing facilities. Some private hospitals and clinics offer the test, along with a doctor visit to explain the meaning of the results. Blood donation centers including the American Red Cross will also test donated blood.

Antibody testing is included in a three-page guide from the FDA about all the kinds of tests available today.

Q: Can I get a test without cost to me?

A: Yes, you can.

Federal law says insurers must cover the cost of a commercial COVID test deemed medically appropriate by a doctor, without cost-sharing by the patient. But there may be charges for related services. You may need to call your insurer and your doctor to get the full picture.

Separately, Minnesota offers residents several different free ways to get saliva or nasal-swab testing, including permanent and pop-up sites. Some residents can use the mail to send saliva samples from home. Options vary depending on where people live. Insurance is not required to get a test, but making an appointment is encouraged.

A full list of the 283 public and private testing locations in Minnesota tracked by the state can be found under "Find Testing Locations" at health.state.mn.us/diseases/coronavirus/testsites.

Joe Carlson • 612-673-4779