What COVID-19 Testing Can and Can’t Tell Us
Posted on Monday, Nov. 23, 2020 at 8:20 am
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?”
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.
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.
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 Test||Antigen Test||Antibody Test|
|Also known as…||Diagnostic test, viral test, molecular test, nucleic acid amplification test (NAAT), RT-PCR test, LAMP test||Diagnostic test||Serological 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 test||Same 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 infection||Diagnoses active coronavirus infection||Shows 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 past||Antigen 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.|