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Best COVID Tests, Accuracy, Where to Find & More -- Boy Getting COVID Test

Answer:

Before we get into specifics, let's start with a quick overview of the types of tests for coronavirus.

Types of COVID-19 Tests

There are basically two types of tests for the coronavirus that causes COVID-19:

Virus test
This test detects the virus (SARS-CoV-2) to determine if you have an active infection and are infectious, i.e., you can spread the virus. Although you can be infectious before showing any symptoms, the virus is best detected during the first week of symptoms (which is about two weeks after becoming infected from exposure) (Sethuraman, JAMA 2020).

The virus test is best done by collecting a sample of mucous from a swab (typically from the nasopharynx or nostril) or saliva. There are two type of virus tests: the PCR and antigen test. Both tests need to be analyzed in a laboratory or with a special rapid, portable machine.

The PCR test uses a technique that amplifies genetic material (RNA) from the virus. This can take as little as a few minutes or several hours. The FDA has begun allowing some at-home sampling kits to be sold by which you can collect your own sample and drop it off or mail it to a lab, which will report the results back to you.

An analysis of tests performed among symptomatic and asymptomatic patients at Vanderbilt University Medical Center showed that the proportion of samples testing positive on PCR tests were twice as high at 2 pm than in the morning, decreasing later in the afternoon and evening. Researchers proposed this may indicate that test accuracy varies by time of day and could have public health implications (McNaughton, medRxiv 2021 -- preprint).

Update: In addition to the many commercial PCR tests that have received Emergency Use Authorization from the FDA, the CDC has been producing its own, FDA-authorized, PCR test. More recently, the CDC developed a newer test that can simultaneously test for and distinguish between COVID, influenza A and influenza B, and, as of January 1, 2022, it will withdraw the older test. Sign in to find out why.

The other type of virus test is the antigen test. It identifies a protein (or "antigen") that is specifically found on the virus. Advantages of the antigen test are that it can provide results in just 15 minutes and can be produced at lower cost, lending itself to wider use in screening. In addition, only a nasal swab is needed from the nostrils, not a much deeper, nasopharyngeal swab. The downside with antigen tests is that they are more likely to provide a false negative result than a gene amplification test; that is, it's more likely to identify your sample as negative when you are actually positive. Consequently, negative results from an antigen test may need to be confirmed with a gene amplification test — but a positive result is highly likely to be accurate. False negatives may also occur with emerging viral variants, if the variants have significant mutations of the target antigen. However, most popular antigen tests in the U.S. target nucleocapsid antigen, which is still present in variants such as Delta and Omicron.

Several home antigen tests are now sold, including Abbott BinaxNow Self Test, BD Veritor, Flowflex, ihealth, InteliSwab, On/Go (AccessBio CareStart), and Quidel QuickVue. There appears to be a significant difference in the accuracy of these tests. [Sign in for our comparison of antigen tests and our Top Pick.]
 

 


Antibody test
This test detects antibodies to the virus and requires blood — either a drop or a vial — to determine if you have been infected in the past and have developed some level of immunity. This test (also called a serology test) can be run in a laboratory or on a test strip, although even test strips must be used in an authorized facility, not at home.

As it takes time to develop antibodies that can be detected, antibody tests are most accurate when performed at least 20 days after the first disease symptoms and may be most accurate (in terms of not missing antibodies that are present) 4 months or longer after a positive virus test. This was shown in study of 486 COVID patients in California in which the likelihood of a positive antibody (IgG) test result increased with time after a positive virus test. Antibody tests were most accurate (~80%) among those ages 40 to 59 years and least accurate (~65%) among those 70+ or under 40. The tests were more accurate for men than women (79% vs 72%) (Vashisht, JAMA Netw Open 2021).

Tests focus on levels of the antibody IgG, which persists without much decline for several weeks, but may include levels of IgM which fall off more rapidly (Sethuraman, JAMA 2020). These tests look for antibodies to specific parts of the virus, namely its spike proteins (proteins on the outside of the virus that can bind to receptors on human cells) or nucleocapsid proteins (proteins inside the virus). An advantage to testing for antibodies to the nucleocapsid is that these antibodies can be easier to detect, however, antibodies to the spike proteins are believed to be more important in conferring immunity against the virus, as these antibodies may block viral entry into cells — although antibodies to nucleocapsid proteins may still serve as proxies for immunity. See Finding the Best COVID-19 Test — Antibody Test to learn which marketed tests target each protein.

Although it is not recommended that antibody tests be relied upon to determine the effectiveness of vaccines, be aware that only tests that focus on antibodies to spike protein would be useful for this purpose because the authorized vaccines generate antibodies only to spike proteins. A negative result on a nucleocapsid antibody test provides no information about the effectiveness of a vaccine although it would suggest that a person has not had COVD-19. The list of authorized antibody tests below indicates whether a test focuses on spike, nucleocapsid, or both types of proteins.

If, at some point, tests for spike protein antibodies are indicated for assessing antibody response to COVID-19 vaccines, those that provide a quantitative or semi-quantitative measurement, will be more useful than those that provide only a yes/no answer. Sign in for more information about antibody tests that focus on the spike protein and are semi-quantitative, including one that is available from a major U.S. laboratory.

Note: Avoid taking large doses — 10,000 mcg or more — of biotin (a B vitamin) for several days before an antibody test, as biotin may skew results.
Sign in to learn which tests may be affected by biotin.
Another way our bodies fight the virus is with T cells. Preliminary research suggests that even if antibody levels are too low to be detected, people previously infected with the virus may produce enough T cell response to provide immunity (Sekine, MediRxiv 2020). However, currently authorized tests do not measure this type of immunity, and one should still apply distancing and health precautions regardless of test results.

Some labs may provide you with an index value that reflects the strength of the antibody signal produced from your test. Higher antibody levels generate higher signals and higher index values. The interpretation of these index values depends on the test used. For example, for a particular test the cut-offs could be "less than 1.01" for negative, "1.01 to less than 1.21" for indeterminate, and "greater than or equal to 1.21" for positive (Theel, J Clin Microbio 2020). Or, there could just be a single cut-off index value of, say, 1.40 for positive, with anything below being negative (Example: Abbott Alinity -- https://www.fda.gov/media/137910/download). If you would like to know your index value, be sure to check that the lab you use provides the value.

Who is checking these tests?
To speed the availability of tests, rather than put these through its normal approval process, the FDA has provided a special emergency use allowance (EUA) for tests that, although imperfect, may be useful at this time. So there are actually no FDA "approved" SARS-CoV-2 virus tests, but a list of "FDA authorized" tests. The FDA allowances are based on data submitted by the test manufacturers, but the National Institutes of Health (NIH) and other government laboratories are now conducting independent tests of these tests and the FDA has been making the results public (see results in the Finding the Best COVID-19 Test section and watch for further announcements in our newsletter.)

Several other organizations around the world have been testing the test and/or certifying virus and antibody tests. The European Union's has been certifying tests, conferring on them its CE (Conformité Européenne) mark, and the Chinese National Medical Products Administration (NMPA) has been doing the same. Researchers in California, Denmark, and elsewhere have been testing the antibody tests. 

Be aware that in June 2020 the FDA warned consumers about at-home antibody tests being sold without FDA clearance or approval and issued warning letters to three companies selling these tests. Some of these tests were falsely labeled as FDA approved. [Update (August 19, 2020): The U.S. Department of Health and Human Services (HHS) announced that CLIA- certified laboratories are no longer required to notify the FDA, nor request its authorization, for tests they develop in-house. It is not clear what information about such tests will be maintained or published. This change could allow for novel tests to become available more quickly but eliminates oversight by the FDA, creating more of a buyer-beware situation. Labs may, voluntarily, still choose to apply to the FDA, and the FDA will continue to publish information about tests submitted this way. If in doubt, ask your doctor or lab if the test you are considering is authorized for use by the FDA. (Links to the FDA information are provided in the Finding the Best COVID-19 Test section.

Where to Get COVID-19 Tests

Virus Test
To date, the FDA has permitted the use of over 90 virus tests. The vast majority must be performed on a sample collected in a medical setting, such as in a doctor's office, a diagnostic laboratory, or a drive-through facility, but the FDA has also begun authorizing at-home sample collection tests for the virus.  

Local testing (often free)
Although you can ask your doctor for a virus test, you may be able to arrange to get a virus test for free from your state or local government. You can also go to a diagnostic laboratory or testing center, including some pharmacies. The test may be covered by your insurance or the government based on an assessment of your risk level. Here are some examples of testing programs around the country.

  • Project Baseline works with community based screening programs in locations in several states to offer free virus testing. You must fill out an online questionnaire and be accepted. You will then be given an appointment at local testing center where a sample will be collected with a self-nasal swab or a nasopharyngeal swab. The project is sponsored by the parent company of Google through its health unit, Verily, and a Google email account is needed to complete questionnaire online.
  • Rite Aid Pharmacies in some locations are participating in Project Baseline, providing testing at no cost to anyone 18+ years of age.
  • CVS (including MinuteClinic and HealthHUB) had originally offered drive-up, rapid testing using the Abbott ID NOW system, a small, portable device that yields results in 13 minutes or less. Unfortunately, this system was been reported to yield a high percentage of false negative results due to lower sensitivity than other systems. That is, a negative result may need to be confirmed using another test (Basu, bioRxiv 2020 preprint). (For more details, see Finding the Best COVID-19 Test, below). Virus testing is still offered, but specimens are now sent to independent, third-party labs for processing, and test results are available in approximately three to four days.
  • Walgreens offers drive-up testing in which you perform your own nasal swab. You sample is sent to a laboratory and you are notified by email or phone when results are available. (Originally results were promised within 24 hours).
  • Kroger Health offers public drive-thru and walk-up COVID-19 testing.


At-home tests
The FDA has authorized several fully self-administered virus tests (providing rapid results) or test kits (to be sent into a lab) for use at home. Currently, two of these (Abbott BinaxNOW Antigen Self-Test and Quidel QuickVue) can be purchased at pharmacies and take about 15 minutes. Note that these will not provide you with a digital pass for events, airlines, or restaurants. Another version of the BinaxNOW Antigen test (the "home" version) provides a digital Navica pass, but this test must be purchased online (at about twice the cost) and many venues may not accept the digital pass.

Update: On October 1, 2021, 200,000 test kits of another COVID-19 home test were recalled due to a manufacturing defect causing false positive results (i.e., indicating that someone has COVID-19 when they do not). For details, including what to do if you've used this home test, sign in to the full answer, which also includes details about four other currently available at-home tests.

Antibody Test
As with virus tests, many laboratories have received FDA approval to conduct antibody tests, some of which are very accurate. Although the FDA has not approved or authorized rapid, home tests for antibodies, many such tests are available in other parts of the world and some have been sold in the U.S. The FDA has authorized one rapid antibody test for use at point-of-care settings, i.e., non-laboratory medical settings such as in medical offices and pharmacies.

Through a local healthcare provider
Your healthcare provider can arrange for you to get an antibody test if deemed appropriate. Blood would be drawn either by your provider or at nearby diagnostic laboratory. Similarly, many walk-in, urgent care centers can arrange for you to have the test, for a fee, which may be covered by your insurance. The samples are typically sent to a commercial laboratory, so results can take a few days. 

Consumer-initiated testing
Be aware than in many cases, the cost of antibody tests may be covered by insurance if ordered by your physician or health care provider. Some labs will require payment for consumer-initiated tests, while others will bill your insurance. Be sure to check the payment policy of the lab you plan to use if requesting your own test. You can also check if your insurance company covers COVID-19 testing. Medicare often covers the full cost of COVID-19 virus and antibody tests. If you are uninsured, health care providers can submit a claim to have virus and antibody tests covered by the Families First Coronavirus Response Act.

QuestDirect allows consumers to request a COVID-19 IgG antibody test and pay for it online ($119 plus a $10.30 physician oversight fee). An appointment is made for a blood draw at one of Quest Diagnostics 2,200 patient service centers and test results are available online one to two days later. Interested consumers must not have experienced symptoms of COVID-19 for at least 10 days. Quest has stated that the testing will initially rely on antibody tests run on the Abbott Architect and EUROIMMUN systems.

Labcorp also allows consumers to request a test directly through its website. According to the website, there is no up-front out-of-pocket cost for consumer initiated tests, but you will be charged a $10 fee for physician oversight services (there is no physician oversight fee if the test order comes directly from your own physician or healthcare provider). Labcorp will "bill the cost of the COVID-19 IgG antibody test directly to your insurance carrier, or if uninsured, to the appropriate government program." Antibody tests offered by Labcorp include Abbott SARS-CoV-2 IgG, Roche Elecsys Anti-SARS-CoV02 (IgG), and DiaSorin SARS-CoV-2. 

You can see how each of these tests compare in the Finding the Best COVID-19 Test section below.

Rapid, home tests
The FDA has not yet approved or authorized of the use of any rapid, home antibody tests but several have been approved by the European Union, which provides its CE mark (Conformité Européenne) and/or by the Chinese National Medical Products Association (NMPA). In addition, research groups have been evaluating these tests. Some of these tests have been marketed in the U.S. without FDA approval or allowance. 

Finding the Best COVID-19 Test

There are now more than 90 virus tests (including a recently approved saliva test) and 22 antibody tests for COVID-19 authorized by the FDA. ConsumerLab has reviewed the data on their performance and assessed which appear to be the best antibody tests for COVID-19. We've added this information for ConsumerLab members. Sign in as a member or become a member now to learn how specific brands of virus and antibody tests compare, which currently appear to be the best, where to get them, and whether any of the tests can identify which variant caused an infection.

What Does a Negative Antibody Test Mean?
If you took a coronavirus antibody test and it came back negative, it can mean one of several things:

  • The test was not sensitive enough to detect antibodies that existed. This is more likely if the test had a sensitivity of less than 100% (see Finding the Best COVID-19 Test — Antibody Test for sensitivities of FDA-authorized tests);
  • You may have never had COVID-19;
  • You took the test too early -- generally less than 20 days after first disease symptoms, although, according to the CDC, some people may take longer; or
  • You didn't develop levels of antibodies high enough to be detected by tests -- which preliminary research suggests may happen in mild and asymptomatic cases (Long, Nature Med 2020).

There is currently not enough data to know if a negative result could result from taking the test too late. More research is needed to determine how long significant levels of antibodies to SARS-CoV-2 persist.

The CDC cautions, "Regardless of whether you test positive or negative, the results do not confirm whether or not you are able to spread the virus that causes COVID-19. Until we know more, continue to take steps to protect yourself and others."

This article will be updated as new information is obtained.

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