Which COVID Test to Use

COVID testing is important. When people know they are positive, they stay home. This prevents the spread of infection. The emergence of new types of tests for COVID may leave you wondering which one to get. Here’s a review of the most common tests available now, the differences between them, and ideas about which test might be best for you.

First of all, when should you get tested? It is recommended that you take a COVID test in the following situations:

• You have symptoms of COVID-19, even after vaccination.
• You have been informed that you are a close contact (within 6 feet for a total of at least 15 minutes) of someone with a confirmed case of COVID, even after vaccination.
• You took part in activities that put you at higher risk, like travel, big gatherings, or crowded indoor settings. 
• You intend to travel or gather and need a negative test in advance.

CLINIC-BASED TESTING

Molecular Tests
Molecular tests, also known as nucleic acid amplification tests (NAAT), identify people who are infected with COVID at the time of testing. They come in a few different forms. PCR stands for polymerase chain reaction. It’s the most accurate test. It’s free and available to all at many testing centers throughout the state, including SVHC’s COVID Resource Center. Most often, a mucous sample is collected on a swab from inside your nose. A second type of test, RT-LAMP, is also a molecular test. LAMP stands for loop-mediated isothermal amplification. Both are sensitive and accurate, and the results produced can be used for official purposes, including shortening a 14-day quarantine. New types of molecular testing may make testing easier and faster for doctor’s offices. The data needed to evaluate the newest methods is still being collected. All of these tests are often free or covered by insurance.

Limitations: None of these tests, nor any test, will determine which variant of COVID you have. Both the PCR and LAMP tests need to be read in a lab, so results take 24 – 36 hours, in most cases.

Antigen Tests
Antigen tests for COVID-19 also identify people who are infected with the COVID-19 virus at the time of the test and, most often, collect a specimen using a nasal swab. They work best within the first 5 to 7 days of having COVID-19 symptoms, when the viral load is generally the highest. One benefit is that they are super fast; they provide results in as few as 15 minutes. In fact, they are sometimes called “rapid tests.”  So, they are used in situations where the test subject already has symptoms, where the subject is among a large group that could have been exposed, and/or when an organization is conducting repeat or routine tests.

Limitations: These tests are not as sensitive as molecular tests, so they are often not accepted for official purposes (including to shorten quarantine, return to school, or for travel). They can yield false negatives. So they may be used to identify people who need a PCR test. If you have symptoms, a negative antigen test generally requires confirmation with a PCR test.

Antibody Tests
Serologic, or antibody, tests identify people who have been infected with the COVID-19 virus in the past and do not show whether a person is infected right now. Serology tests are performed with a doctor’s order and are conducted at a phlebotomy (blood work) lab, rather than at a drive-up or walk-in testing site. The lab tests a blood sample. The results may be interesting to know, but they are not useful for determining whether you are eligible to end quarantine or return to work or school. The results should not be used to establish “proof of immunity.” The results would most useful to healthcare policy advisors, who could gather results from many people as a way to help determine what percentage of the population has been infected.

HOME TESTING

Both molecular and antigen tests are beginning to pop up on pharmacy shelves and for sale online. Many are available on an over-the-counter basis, without a prescription. They can be done at home or anywhere.

Home Antigen Tests
The antigen variety of home tests are quite simple. They resemble a home pregnancy test. Results show up in the form of colored lines within just a few minutes. They are relatively inexpensive, from $24 for a set of two – $38 for one.

Limitations: Insurance plans don’t usually cover home antigen tests. Just like antigen tests administered at a clinic or pharmacy, your home antigen test results will not likely be accepted for official purposes. If you have symptoms, you will likely want to get a PCR test, regardless of what your antigen test result is.   

Molecular Tests
This has all of the benefits of PCR tests performed at a testing site. It might be desirable if you have symptoms and live far from a testing site.

Limitations: The PCR variety of home test is far more expensive, as much as $100 or more, compared to home antigen tests. This test is not as convenient or fast, because you have to send the sample through the mail to a lab; and they need to analyze it before returning your results. The results may not be accepted by organizations hoping to assure that you are COVID-free before returning to work, school, or travel.

All home tests require attention to detail. You should check to be sure the test is not expired. Do not open the testing components until you are ready to use them. Wash your hands with soap and disinfect any surfaces you will be using. Follow the directions carefully. If you don’t do it correctly, your results may not be correct. Instructional videos are available at https://www.cdc.gov/coronavirus/2019-ncov/testing/self-testing.html

Recommendations:

• If you have symptoms or an exposure or you need to present your results to an institution, go to the extra trouble of getting a PCR test in person.
• If you have no symptoms and are looking for assurance—before or after an event, for instance, or you test frequently for your own peace of mind—consider the convenience and rapid results of the home antigen test. Doing so will also save local testing capacity for those who need it most.

If your test is positive, please report results to the Health Department using the Vermont COVID-19 Self-Test Result Reporting Form. Also call your physician and all of your close contacts. Finally, follow instructions for isolation listed here: https://www.cdc.gov/coronavirus/2019-ncov/if-you-are-sick/isolation.html

Karen Bond is the director of Laboratory Services at Southwestern Vermont Medical Center in Bennington.