What COVID-19 Testing Can and Can’t Tell Us

What COVID-19 Testing Can and Can’t Tell Us

Posted on Monday, Nov. 23, 2020 at 8:20 am

En español


What Testing Can and Can't Tell Us While the importance of reliable, accessible testing cannot be overstated, there are limitations to  what testing can  and can’t tell us. Read our blog post:  bit.ly/339Hug2

A critical piece in stopping the spread of COVID-19 is being able to test people for the virus. Through testing, we identify the people who have the virus so they can isolate and prevent spreading the disease to others. As of this posting, nearly half of Dane County residents have been tested for COVID-19 at least once. Our county is very fortunate to be one of the few in the country with consistent, accessible COVID-19 testing available to almost everyone, all for free.


What Testing Can Do

  • Identify someone with COVID-19 infection on the day they are tested
  • Help us begin contact tracing to prevent others from spreading the virus
  • Help us prevent large outbreaks in facilities, businesses, workplaces, and schools
  • Help us understand how many people in the community have the virus
  • Help us identify populations disproportionally affected by COVID-19

What Testing Can’t Do

  • Tell us if someone can safely return to work, school, or their daily routine. People must isolate or quarantine before safely returning to activities.  We recommend against requiring employees to have a negative COVID-19 test before returning to work. Some people can still test positive for weeks following their isolation but are no longer infectious. Requiring a negative test places an unnecessary burden on the employee and may prevent you from providing services due to extended employee absences.
  • Give someone permission to attend an event or gathering. Again, testing only tells us if someone has COVID-19 on the day they are tested. A negative test does not necessarily mean it is safe to gather with others; someone could be exposed, test negative the next day, then test positive the day after that. Tests cost about $100 each and should not be wasted.
  • Serve as a loophole for ignoring precautions. Frequent testing is not a way to avoid taking commonsense precautions like avoiding gathering, wearing a mask, and staying home when you’re sick.
  • Stop the pandemic. Testing is one tool in our toolbox for stopping the spread of the virus, but testing alone can’t stop this pandemic. We also need people to follow Public Health orders, recommendations, and precautions to stop the virus in its tracks.

Scenarios: Should I Get Tested?

Test what you’ve learned with these graphics that ask, “Should I get tested?”
Should I get tested if...I’m going to a wedding this weekend and want to make sure I’m safe?No. Testing only tells you if you had COVID on the day you were tested. A negative test does not necessarily mean it is safe to gather with others.
Should I get tested if...I just want to make sure I'm okay? I like to get tested once per week.No. We do not recommend routine, repeated testing just for peace of mind. Tests cost about $100 each.
Should I get tested if...I have symptoms of COVID-19?Yes! Call your doctor first. If they won't test you or if you do not have a doctor, visit a community test site. Isolate until you get your test results.
Should I get tested if...The person I work next to in our restaurant kitchen tested positive and we're near each other all day?Yes! Call your doctor first. If they won't test you or if you do not have a doctor, visit a community test site. You should quarantine for 14 days even if your test is negative.
Should I get tested if...The person who sits in the cube next to mine has symptoms and got tested, but I don’t know their result?Not yet. You can continue to work but keep an eye out for symptoms. If you develop symptoms, get tested. If their test comes back positive, get tested and quarantine, no matter your result.
Should I get tested if...My neighbor had close contact with someone who later tested positive and before we knew that, he and I hung out and grilled together?No. This is not close contact with someone who has tested positive.
Should I get tested if...A kid in my child’s school tested positive, but they didn’t have contact?No. This is not close contact with someone who has tested positive.
Should I get tested if...My friend tested positive and a few days ago we hung out outside (within 6 feet) but were wearing masks?Yes! Call your doctor first. If they won't test you or if you do not have a doctor, visit a community test site. You should quarantine for 14 days even if your test is negative.


What are My Testing Options?

Visit our testing page to learn more about where you can be tested.


Extra Credit: Learn the Types of Tests Available

There are two types of testing available: diagnostic and antibody.

Diagnostic Testing

A diagnostic test shows if you have active coronavirus infection. In other words, it tells us if you have the virus right now. There are two types of diagnostic tests: molecular tests and antigen tests. Molecular tests, more commonly known as PCR tests (this is the test currently available at the Alliant testing site), work by identifying the virus’s genetic material. Antigen tests work by identifying the virus’s unique proteins.

Antibody Testing

When your body fights an infection, it makes antibodies to respond to the threat. An antibody test tells us if your body has ever tried to fight the virus in the past. These tests cannot tell you if you have a current COVID-19 infection.

We love this table from FDA which outlines the differences of the types of testing available:

Molecular TestAntigen TestAntibody Test
Also known as…Diagnostic test, viral test, molecular test, nucleic acid amplification test (NAAT), RT-PCR test, LAMP testDiagnostic testSerological test, serology, blood test, serology test
How the sample is taken…Nasopharyngeal (the part of the throat behind the nose), nasal or throat swab (most tests) Saliva (a few tests)Nasal or nasalpharyngeal swab (most tests)Finger stick or blood draw
How long it takes to get results…Same day (some locations) or up to a week (longer in some locations with many tests)Some may be very fast (15 – 30 minutes), depending on the testSame day (many locations) or 1-3 days
Is another test needed…This test is typically highly accurate and usually does not need to be repeated.Positive results are usually highly accurate, but false positives can happen, especially in areas where very few people have the virus. Negative tests should always be interpreted in the context of the exposure history and clinical presentation of person being tested.

In most cases, negative antigen tests are considered presumptive and should be confirmed with a RT-PCR test.

A negative result in a patient with a low pre-test probability of infection is more likely to be a true negative and confirmatory testing may not be needed unless important for clinical management or infection control. See CDC rapid antigen testing for more discussion.
Sometimes a second antibody test is needed for accurate results.
What it shows…Diagnoses active coronavirus infectionDiagnoses active coronavirus infectionShows if you’ve been infected by coronavirus in the past
What it can’t do…Show if you ever had COVID-19 or were infected with the virus that causes COVID-19 in the pastAntigen tests are more likely to miss an active COVID-19 infection compared to molecular tests. Your health care provider may order a molecular test if your antigen test shows a negative result but you have symptoms of COVID-19.