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COVID-19

Testing

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TYPES OF COVID-19 TESTS

There are different types of COVID-19 tests.

  • Viral tests (NAAT and antigen) are swab or saliva tests that look for current infection. Most self-tests are antigen tests.
  • Antibody tests are blood tests that look for past infection.

Only viral tests are recommended to see if you are currently infected with COVID-19.

Viral tests are swab or saliva tests.

  • They can show if you have a current infection.
  • There are two main types of viral tests: antigen tests and nucleic acid amplification tests (NAATs):
    • Antigen tests are rapid tests that give results in 15-30 minutes.
      • Antigen tests are less accurate than NAATs. This means that they are more likely to give false results, especially false negatives. Since antigen tests are less accurate, it is recommended that negative tests be repeated at least 48 hours later. See FDA instructions on repeat testing.
      • Sometimes a follow-up NAAT may be recommended to confirm an antigen test result.
      • Antigen tests are the best test for people who have tested positive in the last 90 days.

    • NAATs, such as PCR and LAMP tests, are usually performed in a laboratory.
      • PCR tests are the most accurate type of NAAT test for COVID-19. NAAT tests are less likely to give false results than antigen tests. They are sometimes used to confirm the results of rapid tests.
      • NAATs detect genetic material from the COVID-19 virus. If you get a COVID infection, this genetic material can stay in your body for up to 90 days. For this reason, NAATs are not recommended for people who have had COVID until 90 days have passed since their first positive test.

  • Most self-tests, or at-home tests, are antigen tests. It is very important to follow the manufacturer’s step-by-step instructions exactly. See Self-tests-free kits and how to test to learn more, including how to tell if your test is good to use after it is past its expiration date.
  • See Understanding Your Viral Test Result and What to do Next for more information.

Antibody tests (also known as serology tests) are blood tests.

  • They might tell you if you had an infection in the past, but they cannot tell you when.
  • They should not be used to test for a current infection or to tell if you are protected from getting COVID-19 in the future.
VIRAL TESTS

(swab or saliva tests)
Looks for current infection

ANTIBODY TEST

(blood tests)
Looks for past infection

NUCLEIC ACID AMPLIFICATION TEST (NAAT)
(molecular tests e.g., PCR and LAMP*)

ANTIGEN TEST
(most self-tests are antigen tests)

ANTIBODY TEST
(serologic test or serology)

How the test works

Detects genetic material (RNA) within the COVID-19 virus

Detects proteins (or antigens) on the surface of the COVID-19 virus

Detects antibodies made by the immune system

How the test is done

Saliva, or swab from nose or throat

Swab from nose or throat

Blood from arm or finger stick

How long it takes to get results

Same day and up to 3 days. Some are rapid (around 20 minutes)

Most are rapid, around 10-30 minutes

Same day and up to 3 days

Over the counter self-tests

A few companies make them

Many companies make them

Not available

*Includes PCR (e.g., Reverse-Transcriptase Polymerase Chain Reaction - RT-PCR) and Loop-Mediated Isothermal Amplification (LAMP)

When to Get a Test

  • If you have COVID-19 symptoms.
  • If you have been a "close contact" to someone with COVID-19. See ph.lacounty.gov/covidcontacts.
  • If you have COVID-19, to see if you can end isolation early (on Day 6 or later). It is best to use an antigen test for this. See ph.lacounty.gov/covidisolation.
  • Before and after travel. See CDC Travel for current recommendations.
  • Before and/or after attending a gathering or event, especially if you will be around people who are at high risk for severe illness.
  • For screening (schools, workplaces, venues, etc.).
  • If recommended by a healthcare professional or Public Health.

Note: There may be other settings that have their own testing requirements.

If you had COVID-19 within the last 90 days, you should test if you have symptoms of COVID-19. You should also test if you are a close contact to someone with COVID-19 and it has been 31-90 days since your first positive test. Otherwise, testing is not usually recommended. If you do test within 90 days of your first positive COVID-19 test, use an antigen test rather than a NAAT.

Understanding Your Viral Test Results and What to do Next

Talk with your doctor to make sure you understand what your test result means and any next steps. If you took a self-test, read the manufacturer’s instructions on how to interpret the test results. If you need advice about what to do next, you can also call the DPH COVID-19 information line at 1-833-540-0473.

Your COVID-19 Test was POSITIVE (POS)

The test detected the COVID-19 virus. It is very likely you have COVID-19 and could spread it to others. For instructions on what to do next click on the situation that applies to you.

If you have symptoms of COVID-19

  • Isolatestay home away from others and follow instruction: ph.lacounty.gov/covidisolation.
  • Tell all of your close contacts that they have been exposed: give them the Instructions for Close Contacts available at ph.lacounty.gov/covidcontacts.
  • Answer the call from LA Public Health: Help slow the spread of COVID-19 by answering if you get a call from “LA Public Health” or 1-833-641-0305. You can also call 1-833-540-0473.
  • If you did a self-test and have questions about isolation or you need referrals/resources or help to notify your contacts, call the DPH COVID-19 information line at 1-833-540-0473.

Important: If you are at high risk for getting very sick from COVID-19 you may be able to get medicine to help keep you out of the hospital. Contact a doctor right away even if your symptoms are mild. Don’t delay: the medicines work best when they are given as soon as possible after symptoms start. See ph.lacounty.gov/covidmedicines for more information.

If you don’t have symptoms of COVID-19

  • Isolate- stay home away from others and follow instructions: ph.lacounty.gov/covidisolation.
  • Tell all of your close contacts that they have been exposed: give them the Instructions for Close Contacts available at ph.lacounty.gov/covidcontacts.
  • Answer the call from LA Public Health: Help slow the spread of COVID-19 by answering if you get a call from “LA Public Health” or 1-833-641-0305. You can also call 1-833-540-0473.
  • If you did a self-test and have questions about isolation or you need referrals/resources or help to notify your contacts, call the DPH COVID-19 information line at 1-833-540-0473.

Important: If you are at high risk for getting very sick from COVID-19 you may be able to get medicine to help keep you out of the hospital. If you develop any symptoms, even if they are very mild, contact a doctor right away. Don’t delay: the medicines work best when they are given as soon as possible after symptoms start. See ph.lacounty.gov/covidmedicines for more information.


Your COVID-19 Test was NEGATIVE (NEG)

A negative COVID-19 result means the test did NOT detect the COVID-19 virus at the time you took the test. If you used a self-test, see FDA instructions on repeat testing.

For instructions on what to do next click on the situation that applies to you.

If you have symptoms of COVID-19

Important note: If you have been in close contact to a person with COVID-19 within the past 10 days, please follow the Instructions for Close Contacts at ph.lacounty.gov/covidcontacts.

It is possible that the test is wrong and that you are infected. This can happen for many different reasons including if the test was taken too early, if your specimen sample wasn’t collected well, or if the amount of virus was too low to be detected by the test. 

If you have symptoms AND you have a negative test, stay home until at least*:

  • You have been fever-free 24 hours without the help of fever-reducing medicines.

*If your negative test is an antigen test and/or self-test, it is recommended that you keep staying away from others and take at least one more test 48 hours later. This is because these tests are more likely to miss early infections. If it is a self-test, make sure you read and follow all test instructions correctly. See FDA instructions on repeat testing.

Note: Even with a negative test, your doctor may still diagnose you with COVID-19 based on your history, symptoms, and your physical examination (if done).

If you don’t have symptoms of COVID-19

Important note: If you have been in close contact to a person with COVID-19 within the past 10 days, please follow Instructions for Close Contacts at ph.lacounty.gov/covidcontacts

If you have no symptoms and you are not a close contact, it is unlikely you have COVID-19*.

  • Keep safe and help prevent the spread of COVID. See Reducing Risk for information.

*If your negative test was a self-test, make sure you read and follow all test instructions correctly. Some self-tests are designed to be used in a series (also known as serial testing). Multiple negative tests increase the confidence that you are not infected with the virus that causes COVID-19.

TESTING FOR PAST INFECTION: ANTIBODY TESTS (serology)

COVID-19 antibody tests (also known as serology tests) are blood tests that are used to look for antibodies to SARS-COV-2 (the virus that causes COVID-19). If we get COVID-19 or a COVID-19 vaccine our body’s immune system responds. It makes antibodies and prepares our immune cells to be ready to fight the virus in the future.

COVID-19 antibody tests do not look for the actual SARS-CoV-2 virus itself. They can be used to help figure out if someone was infected with COVID-19 in the past. It takes about one to three weeks after becoming infected for the body to make enough antibodies to be found by a test. Some people may take even longer, and some people who were infected with COVID-19 may never develop antibodies. NONE of the currently authorized tests are recommended to see if people have been successfully vaccinated against COVID-19.

COVID-19 antibody tests cannot tell a person:

  • When or if they definitely had COVID-19
  • Whether or not they are protected (immune) from COVID-19
  • Whether it is safe to travel or spend time with other people
  • Whether they need to isolate or quarantine
  • Whether they should or should not get vaccinated
  • Whether or not their vaccine is working.

Antibody tests are not 100% accurate, so false results may occur. Talk to your doctor before being tested for antibodies. Your doctor can help you decide if you should be tested and, if you are tested, tell you what your results mean. To learn more about antibody tests, visit the CDC webpage.

MORE INFORMATION

  • CDC COVID-19 Testing: webpage with links to pages on types of tests and FAQs
  • FDA Coronavirus Basics: webpage explains the different types of tests, and how they are performed and approved.

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Public Health has made reasonable efforts to provide accurate translation. However, no computerized translation is perfect and is not intended to replace traditional translation methods. If questions arise concerning the accuracy of the information, please refer to the English edition of the website, which is the official version.

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