MIL-OSI USA: Coronavirus Disease 2019 Testing Basics

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Source: US Food and Drug Administration-1

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You’ve probably heard a lot about coronavirus disease (COVID-19) testing. If you think you have COVID-19 and need a test, contact your health care provider or local health department immediately. You can also find a community testing site in your state, or buy an FDA-authorized at-home test. Some FDA-authorized at-home tests give you results within minutes. Others require you to mail the sample to a lab for analysis.

Understanding COVID-19 testing is key to making an informed decision that meets your needs.

Types of Tests

There are different types of tests – diagnostic tests and antibody tests.

Diagnostic tests can show if you have an active COVID-19 infection and need to take steps to quarantine or isolate yourself from others. Molecular and antigen tests are types of diagnostic tests than can detect if you have an active  COVID-19 infection. Samples for diagnostic tests are typically collected with a nasal or throat swab, or saliva collected by spitting into a tube.

Antibody tests look for antibodies in your immune system produced in response to SARS-CoV-2, the virus that causes COVID-19. Antibody tests should not be used to diagnose an active COVID-19 infection. Antibodies can take several days or weeks to develop after you have an infection and may stay in your blood for several weeks or more after recovery. Samples for antibody tests are typically blood from a finger stick, or blood drawn by your doctor or other medical personnel.

Getting Tested

If you are tested, you should quarantine and isolate yourself at home until you receive your test results and follow the advice of your health care provider or a public health professional.

When should I get a test?

  • If you have symptoms of COVID-19, even after vaccination
  • If you have had close contact (within 6 feet for a total of 15 minutes or more) with someone with confirmed COVID-19, even after vaccination
  • If you took part in activities that put you at higher risk for COVID-19 because you could not socially distance as needed, such as travel, attending large social or mass gatherings, or being in crowded indoor settings
  • If you have been asked or referred to get tested by your health care provider, or local or state health department

Your school, workplace or community may also establish a screening program, in which they test individuals who are part of a group (at work, at school) even if there is no reason to suspect those individuals are infected with COVID-19. The FDA issued more information about screening programs in this fact sheet.

To find a local testing site, you should contact your health care provider or go to your state or local health department’s website.

Do COVID-19 tests check for the delta and other variants?

There are no authorized COVID-19 antigen or molecular tests that specifically report the presence of the SARS-CoV-2 delta variant. Currently, COVID-19 tests are designed to check broadly for the SARS-CoV-2 virus, including the SARS-CoV-2 delta variant.  It is common for all viruses to change and mutate over time, resulting in different virus strains. The FDA works closely with test developers to identify potential impacts of virus mutations on FDA authorized COVID-19 tests and help ensure there is minimal impact on test performance.

Local, state, and federal public health agencies, including the Centers for Disease Control and Prevention, track the SARS-CoV-2 virus variants so we can understand which strains of the virus are spreading. 

Health care providers treat patients who have COVID-19 based on the patient’s symptoms and not based on the strain of virus. For more information on treatment options see Know Your Treatment Options for COVID-19 and discuss your symptoms with a health care provider.
 

Ordering a Test

Many tests, including some home collection and at-home tests, require a prescription or order from a health care provider.

Prescription Tests – Health care providers can determine whether you need a test, and ensure you get the most appropriate test and that you know what the results mean. For example, certain tests are authorized only for people suspected of having COVID-19 or for people with COVID-19 symptoms that started within a certain number of days. A health care provider can help determine which test is best for your situation. Prescription-only home collection and at-home tests may require you to answer some questions online so that a health care provider can determine whether to prescribe or order a specific test.

Non-Prescription Tests – Some tests are available without a prescription. Home collection and at-home tests available without a prescription may be called “direct-to-consumer” (DTC) or “over-the-counter” (OTC). DTC and OTC tests may be available to purchase at a pharmacy or online, but they may not be available everywhere.

Home Collection and At-Home Tests

Can I get an at-home test? What is the difference between home collection and at-home tests? What kit do I need to order? To answer these questions, it is important to understand the differences in COVID-19 tests, and home collection tests versus at-home tests.

Why is this important? These differences determine where the sample is collected, where the test is processed, and how quickly you find out the results. While at-home tests may be the quickest and most convenient option, they may not be the most appropriate for all situations.

If you want to be sure the test you are buying is authorized by the FDA, visit our tables of molecular, antigen, and serology and adaptive immune response in vitro diagnostic emergency use authorizations (EUA) for more information.

Using the search box in the EUA tables you can use keywords to search and filter the type of test or collection kit you are looking for. Using this search, as new tests are authorized for use, consumers can access up-to-date information on authorized tests and collection kits.

Types of Samples

Different tests are authorized to be used with different types of samples. The most common sample types are:

Swab samples use a swab (similar to a long Q-Tip) to collect a sample from the nose or throat. The types of samples include:

  • Anterior Nares (Nasal) – takes a sample from just inside the nostrils
  • Mid-turbinate – takes a sample from further up inside the nose
  • Nasopharyngeal – takes a sample from deep inside the nose, reaching the back of the throat
  • Oropharyngeal – takes a sample from the middle part of the throat (pharynx) just beyond the mouth

Saliva samples are collected by spitting into a tube rather than using a nose or throat swab.

Blood samples are only used to test for antibodies and not to diagnose COVID-19. Venous blood samples are typically collected at a doctor’s office or clinic. Some antibody tests use blood from a finger stick.

Pooled Sample Testing

One way for laboratories to test more people for COVID-19 is by combining samples from several people into one sample and testing them together, also called “pooling.” Pooling is most helpful in areas where most samples are expected to be negative. This saves time and test materials when only a very small number of positives are expected, allowing labs to test more samples.

If the test is negative, or doesn’t detect SARS-CoV-2, then none of the people whose samples were included in the pooled sample are likely to have an active COVID-19 infection.

If the test is positive, showing the presence of the virus that causes COVID-19, everyone is retested separately, either by taking a new sample or testing a remaining portion of the original sample, to find the samples that are positive.

Understanding Your Test Results

Generally, for diagnostic tests, a negative result means the test did not detect the SARS-CoV-2 virus, and a positive result means the test did detect the SARS-CoV-2 virus and you are very likely to have COVID-19.

However, no test is perfect. There is always a chance that a test will return a false result. For diagnostic tests, a false negative means the test says you don’t have COVID-19 but you are infected, and a false positive means that the test says you have COVID-19 but you are not infected.

Because of this, even if you receive a negative result, you should keep practicing preventive measures, such as distancing, washing hands, and wearing masks,  to reduce the risk of spreading COVID-19.

If you are sick, you should stay home and isolate from others, even if you receive a negative test result. Talk with your health care provider to determine if you should be retested or for advice on managing your symptoms.

For serology tests, a negative result means the test did not detect antibodies to the virus that causes COVID-19.  A positive result means the test did detect antibodies to the virus that causes COVID-19, and it is possible that you had a recent or prior COVID-19 infection and you have developed an adaptive immune response to the virus. 

We do not know how long antibodies stay in the body following infection with the virus that causes COVID-19. We do not know if antibodies give you protective immunity against the virus, so results from a serology test should not be used to find out if you have immunity from the virus. The FDA cautions patients against using the results from any serology test as an indication that they can stop taking steps to protect themselves and others, such as stopping social distancing or discontinuing wearing masks.

Key Terms

  • SARS-CoV-2: the virus that causes COVID-19
  • COVID-19: the illness caused by the SARS-CoV-2 virus
  • Home Collection Test: sample is collected at home but analyzed in a laboratory
  • Direct to Consumer (DTC) Test: home collection tests available without a prescription, but the sample is analyzed in a laboratory
  • At-home Testing: consumer completes sample collection and testing at home
  • Over the Counter (OTC) Test: consumer completes sample collection and testing at home, without a prescription
  • Diagnostic Test: shows if you have an active COVID-19 infection
  • Molecular Test: a diagnostic test that detects genetic material from the virus
  • Reverse Transcription Polymerase Chain Reaction (RT-PCR): one type of molecular diagnostic test
  • Nucleic Acid Amplification Test (NAAT): one type of molecular diagnostic test
  • Antigen Test: a diagnostic test that detects specific proteins from the virus
  • Antibody (Serology) Test: detects antibodies that are made by your immune system in response to a threat, such as a specific virus; not used to diagnose active infection
  • Pooled Sample Testing: testing several samples together

Report Adverse Events

The FDA encourages health care professionals and patients to report adverse events or side effects as well as performance issues related to the use of COVID-19 tests or other medical products to the FDA’s MedWatch Safety Information and Adverse Event Reporting Program:

  • Complete and submit the report online through the FDA’s MedWatch website.
  • Download the form or call 1-800-332-1088 to request a form, then complete and return to the address on the form or submit by fax to 1-800-FDA-0178.

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