Allegheny County and state officials have each begun including antigen test results in daily updates of covid-19 case counts.

Antigen tests are different from traditional covid-19 tests – but they are both used to indicate an infection.

For months, the covid-19 test of choice was the PCR test, which searches for nucleic acid from the virus that causes covid-19 using mucus samples from inside of the nose.

Antigen tests, on the other hand, search for the proteins and lipids in the virus that causes covid-19.

Wells said antigen tests cannot amplify the covid-19 genetic material the way PCR tests can; therefore, an individual must have more of the virus present for the antigen test to pick it up.

While PCR and antigen tests are meant to detect a current infection, antibody tests are used to see if an individual had been exposed to covid-19 in the past.

Maggi Mumma, a Pennsylvania Department of Health spokeswoman, said the change was because of an updated definition for covid-19 from the Council of State and Territorial Epidemiologists – a nonprofit that represents epidemiologists and advocates for public health policies.

The Allegheny County Health Department began using antigen tests to identify probable cases on Aug.

Previously, cases with positive antigen tests were counted as probable only if the subject also had covid-19 symptoms or had close contact with a known case.

Antigen tests were authorized for emergency use by the Food and Drug Administration, but Wells said the tests have been known to produce both false positives and false negatives – Ohio Gov.

Some states with travel restrictions will allow visitors if they have tested negative, but won’t accept antigen tests as the testing method, Wells said.

That’s why antigen test results should be considered probable cases, not confirmed, Wells said.

He said they are best used for younger individuals like college students, who are not at high risk of death by the disease, and positive cases should also be verified later using a PCR test.