With kids back in school and people heading back to the office, something as minor as a cough or runny nose might lead us to get tested for COVID.
A lot has changed since the early days of the pandemic when the only way to get tested was to line up at a testing site. Today, there are many different options.
Which test is best?
What You Need to Know to Make the Right
Coronavirus Testing Choice
There are hundreds of different COVID diagnostic tests on the market. But they all fall into one of two categories:i
- PCR tests. Also known as molecular tests. They detect genetic material from the virus using a lab technique called polymerase chain reaction (PCR).
- Antigen tests. Also known as rapid tests. They detect certain virus proteins.
Samples are collected the same way for both—through a nasal swab or saliva collected by spitting into a tube.
PCR tests were the first test developed to diagnose COVID-19. They are still the most widely used. It’s what you will likely get if you go to a government-sponsored testing site or to a doctor’s office.
Samples are sent to a lab for processing. PCR test results usually take one to seven days.
Antigen tests, on the other hand, are usually processed on the spot. You can get the results in about 15 minutes. Do-it-yourself at-home antigen tests are now widely available, although shortages have been reported in some areas. They are somewhat similar to home pregnancy tests.
You take a sample with a nose swab and insert it into a test card. Then you wait 15 minutes. If an indicator line appears, it means you are positive. If no line appears, you are negative.
The tests are sold at pharmacy chains, big box stores, and on Amazon. They usually come in packs of two for about $25.ii
Their main advantages are convenience and speed. You get your results in just minutes. And you can take the test at home. But there is a tradeoff in accuracy.
Antigen tests have higher rates of false-negative results than PCR tests. In other words, they may show that you are negative when you actually do have the virus.
Both antigen and PCR tests rarely show false-positives. In only about 1% of tests do they err by indicating a person is positive for COVID when they don’t actually have it.
How Accurate Are COVID Tests?
Here are accuracy rates for three widely available at-home antigen tests:iii
Quidel QuickVue: 83% accurate. In other words, 17% of people tested get negative results when they actually have COVID.
Abbott BinaxNOW: 84% accurate. 16% of people tested get false-negatives.
Ellume COVID-19 Home Test: 91% accurate. The false-negative rate is about 9%.
How do PCR tests stack up?
Most studies show that PCR tests are accurate more than 95% of the time.iv
“PCR tests are considered the most accurate available,” said Dr. Richard Martinello. He is an infectious disease specialist at Yale Medicine.v
Another advantage to PCR tests is that they are often covered by insurance. At-home antigen tests usually aren’t.vi
Multiplex PCR tests are another option. They not only test for COVID but also the flu. Some tests check for respiratory syncytial virus (RSV) as well. RSV is a common respiratory infection. It is particularly prevalent in children. The symptoms are usually like a cold but can be more severe.vii viii
People who feel sick and test negative for COVID often wonder what is causing their symptoms if it’s not coronavirus. A multiplex test may provide the answer. They are available at doctor’s offices and medical clinics. They are usually covered by insurance.
Do You Have Delta?
No widely available COVID test will tell you if you have Delta or another variant of the virus. Detecting variants requires genetic testing done in a lab.
The CDC monitors variants by getting a selection of positive COVID samples from around the country and sending them to specialized labs. There they are genetically sequenced to identify the strain of the virus. Variant testing is usually not available for individual patients.
If you tested positive in the past month, it is extremely likely you had the Delta variant. By mid-August, it was responsible for 98% of COVID cases in the U.S.ix
What About Antibody Tests?
Another common COVID test involves antibodies. It does NOT tell you if you have an active infection. It reveals if you’ve been infected in the past.x
An antibody test requires a blood draw. It is usually done in a doctor’s office or hospital.
Antibody tests do not provide a reliable indication that your vaccine is working.
That’s because the antibodies generated by the vaccine can differ from those caused by an infection. If you get an antibody test after getting vaccinated, the results are not considered meaningful. You might test positive because of a previous infection or because of the vaccine—it depends on the type of antibody the specific test detects.xi xii xiii
What Type of Test Should You Get?
In most situations, either a PCR or rapid antigen test will be fine. “A lot of it depends on access and what is readily available to you,” said Dr. Martinello.xiv
However, in a high-stakes situation, such as when you are visiting an elderly relative, you may want the increased accuracy of a PCR test, he said.
If you are getting tested because you think you’ve been exposed to COVID—say you went to crowded a concert or a co-worker tested positive—don’t get tested immediately after the exposure.
“You don’t want to take any COVID test—antigen or PCR—the next day,” Dr. Martinello said. “You should wait three to five days after potential exposure.” Otherwise, you may get a false-negative because you won’t yet have a detectable level of virus in your body.
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