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Metro Health: Self-swab tests may not be as accurate as professionally conducted tests

COVID-19 tally consists of nasal swab, antigen tests

In this Wednesday, May 6, 2020 photo a woman swabs the inside of her mouth during a self administered coronavirus test at a drive through testing site in a parking lot in the Woodland Hills section of Los Angeles. The city of Los Angeles is providing free coronavirus tests to anyone who wants one regardless of whether they have symptoms. The offer reflects a parting with state guidelines after the mayor partnered with a startup testing company. The test the city is offering is easier to administer and doesn't require the scarce supplies that have created bottlenecks for expanded testing across California. (AP Photo/Richard Vogel)
In this Wednesday, May 6, 2020 photo a woman swabs the inside of her mouth during a self administered coronavirus test at a drive through testing site in a parking lot in the Woodland Hills section of Los Angeles. The city of Los Angeles is providing free coronavirus tests to anyone who wants one regardless of whether they have symptoms. The offer reflects a parting with state guidelines after the mayor partnered with a startup testing company. The test the city is offering is easier to administer and doesn't require the scarce supplies that have created bottlenecks for expanded testing across California. (AP Photo/Richard Vogel) (Copyright 2020 The Associated Press. All rights reserved.)

SAN ANTONIO – San Antonio health officials are advising that not all COVID-19 tests yield accurate results.

Dr. Colleen Bridger, interim director of the Metropolitan Health District and assistant city manager, said self-tests may not produce precise results in comparison to those administered by professionals.

“The self-tests are slightly less accurate than the health professional conducted tests,” Bridger said during the city and county’s daily briefing on Tuesday. “Generally speaking, we recommend you go to one of our sites where a health professional could administer the test or go to your own private physician’s office where they can do it.”

She did not detail which self-swab tests are the most accurate because there’s “a spectrum of those tests.”

Those who are awaiting results should quarantine themselves, out of caution that they do have a positive result, she added.

What you need to know about COVID-19 testing according to UT Health experts

Health officials use two types of tests for the virus: polymerase chain reaction diagnostic (PCR) tests and antigen tests, according to UT Health San Antonio.

PCR tests consist of a 6-inch swab inserted into the nasal cavity. Antigen tests use blood samples, and those results could return within minutes, according to UT Health.

Those antigen tests, though, have low sensitivity to the coronavirus and may not be as accurate. PCR tests have a higher sensitivity and are considered more accurate, health officials say.

In its COVID-19 tally for Bexar County, Metro Heath includes confirmed cases with PCR tests and positive results from antigen tests.

No, entire households are not included in COVID-19 count in San Antonio

The city does not count entire households as cases, and does not include antibody tests in the case count, Metro Health spokesperson Michelle Vigil said.

If a person wants to receive an antibody test, they should make sure the test has been approved by the Food and Drug Administration, according to Metro Health.

Antibody tests, or serological tests, help identify who has been infected with or exposed to COVID-19.

While the Texas Department of State Health Services includes antibody counts on its dashboard, Vigil said Metro Health is not required to report antibody tests to the state.

Mayor reports 439 new COVID-19 cases Wednesday, bringing the total case tally to 12,504.

She added antibody tests may not be reliable, and those tests may lead people to believe they’re immune when they may not be.

Read also:

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KSAT Explains: How COVID-19 pandemic has spotlighted longstanding inequities and socioeconomic issues in San Antonio

Data: 74% of all San Antonio’s COVID-19 cases were reported in June


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