I've heard about antibody testing for COVID-19. What is antibody testing? Is it the same as testing to diagnose COVID-19?

回答 William F. Marshall, III M.D.

With all the talk about coronavirus disease 2019 (COVID-19) testing in the news, it's not surprising that there's confusion about tests and how they differ. Antibody testing determines whether you had COVID-19 in the past and now have antibodies against the virus. A test to diagnose COVID-19 determines if you currently have the disease. Here's what you need to know about testing.

When is antibody testing done and why is it important?

Antibody testing, also known as serology testing, is usually done after full recovery from COVID-19. Eligibility may vary, depending on the availability of tests. A health care professional takes a blood sample, usually by a finger prick or by drawing blood from a vein in the arm. Then the sample is tested to determine whether you've developed antibodies against the virus. The immune system produces these antibodies — proteins that are critical for fighting and clearing out the virus.

If test results show that you have antibodies, it indicates that you were likely infected with COVID-19 at some time in the past. It may also mean that you have some immunity. But there's a lack of evidence on whether having antibodies means you're protected against reinfection with COVID-19. The level of immunity and how long immunity lasts are not yet known. Ongoing studies will eventually reveal more data on this.

The timing and type of antibody test affects accuracy. If you have testing too early in the course of infection, when the immune response is still building up in your body, the test may not detect antibodies. So antibody testing is not recommended until at least 14 days after the onset of symptoms. The U.S. Food and Drug Administration (FDA) authorized specific antibody tests, but tests with questionable accuracy are still on the market.

Another benefit of accurate antibody testing is that people who've recovered from COVID-19 may be eligible to donate plasma, a part of their blood. This plasma could be used to treat others with severe disease and boost the ability to fight the virus. Doctors call this convalescent plasma.

What tests are used to diagnose COVID-19?

The FDA approved these types of tests for diagnosing a COVID-19 infection:

  • PCR test. Also called a molecular test, this COVID-19 test detects genetic material of the virus using a lab technique called polymerase chain reaction (PCR). A fluid sample is collected by inserting a long nasal swab (nasopharyngeal swab) into your nostril and taking fluid from the back of your nose or by using a shorter nasal swab (mid-turbinate swab) to get a sample. In some cases, a long swab is inserted into the back of your throat (oropharyngeal swab), or you may spit into a tube to produce a saliva sample. Results may be available in minutes if analyzed onsite or a few days — or longer in locations with test processing delays — if sent to an outside lab. PCR tests are very accurate when properly performed by a health care professional, but the rapid test can miss some cases.
  • Antigen test. This COVID-19 test detects certain proteins in the virus. Using a long nasal swab to get a fluid sample, antigen tests can produce results in minutes. Because these tests are faster and less expensive than PCR tests, antigen tests may be more practical to use for large numbers of people. A positive antigen test result is considered accurate when instructions are carefully followed, but there's an increased chance of false-negative results — meaning it's possible to be infected with the virus but have a negative result. Depending on the situation, the doctor may recommend a PCR test to confirm a negative antigen test result.

Certain COVID-19 test kits authorized by the FDA allow you to collect the sample at home and then send it to a lab to be analyzed. One at-home COVID-19 test that's authorized by the FDA provides fast results at home. This nasal swab test requires a doctor's prescription. At-home PCR tests are likely more accurate than at-home antigen tests are, but a sample collected by a trained professional may be more reliable. The FDA warns consumers that some scammers are promoting unauthorized COVID-19 tests, so only get a test that's authorized by the FDA.

What do I do if I'm interested in a COVID-19 diagnostic test or an antibody test?

You can contact your local or state health department or visit the department's website for information on testing. If you have symptoms of COVID-19, contact your doctor to discuss your situation and find out how to prepare for your appointment before seeking a COVID-19 test in person.

A COVID-19 diagnostic test is recommended if you have symptoms or you've had close contact with someone who tests positive for the COVID-19 virus or is suspected of having the virus. To get antibody testing, you have to be fully recovered from COVID-19. But in some communities, people who never had symptoms of COVID-19 may be able to get tested. Some have positive results, meaning they likely were infected by the COVID-19 virus at some time.

Access to either test depends on where you live, test availability and whether you're viewed as eligible. In the U.S., collaborative efforts to make more tests available are ongoing. The nationwide goal is to test more people as more tests become available.

How can diagnostic and antibody testing help reduce the spread of COVID-19?

With COVID-19 diagnostic testing, people who test positive and have symptoms can get care earlier. Contacts can be traced and self-isolation or quarantine started sooner to help stop the spread of the virus.

But no COVID-19 test is 100% accurate. It's possible to test negative yet actually be infected (false-negative result) or to test positive and not be infected (false-positive result). So it's vital to continue to follow COVID-19 guidelines from the Centers for Disease Control and Prevention, such as social distancing and wearing a mask when appropriate, until further notice.

Results of antibody tests indicate how many people had COVID-19 and recovered, including those who didn't have symptoms. This aids in determining who might have immunity, though to what extent and for how long is not yet known.

With

William F. Marshall, III M.D.

Nov. 24, 2020 See more Expert Answers

也可查阅

  1. Can COVID-19 (coronavirus) spread through food, water, surfaces and pets?
  2. COVID-19 and vitamin D
  3. Safe cancer treatment during the COVID-19 pandemic
  4. Cancer treatment during COVID-19: How to move ahead safely
  5. Convalescent plasma therapy
  6. Coronavirus safety tips for going out
  7. COVID-19
  8. 冠状病毒疾病:这是什么疾病,如何自我保护?
  9. Coronavirus grief
  10. Coronavirus travel advice
  11. Coronavirus vs. flu: Similarities and differences
  12. Cough
  13. Herd immunity and coronavirus
  14. COVID-19 and high blood pressure
  15. COVID-19 and pets
  16. COVID-19 and the risk of suicide
  17. COVID-19 and your mental health
  18. COVID-19 antibody testing
  19. COVID-19 and holidays
  20. COVID-19 (coronavirus) drugs: Are there any that work?
  21. COVID-19 (coronavirus) in babies and children
  22. Long-term effects of COVID-19
  23. COVID-19 (coronavirus) stigma: What it is and how to reduce it
  24. COVID-19 (coronavirus) vaccine
  25. COVID-19 tests
  26. COVID-19: How much protection do face masks offer?
  27. Coping with unemployment caused by COVID-19
  28. COVID-19 (coronavirus): Quarantine, self-isolation and social distancing
  29. COVID-19: Social distancing, contact tracing are critical
  30. COVID-19: Who's at higher risk of serious symptoms?
  31. Debunking coronavirus myths
  32. Diarrhea
  33. Extracorporeal membrane oxygenation (ECMO)
  34. Surgery during the COVID-19 pandemic
  35. Fever
  36. Fever: First aid
  37. Fever treatment: Quick guide to treating a fever
  38. Getting safe emergency care during the COVID-19 pandemic
  39. Kids, loneliness and COVID-19
  40. Honey: An effective cough remedy?
  41. How to take your pulse
  42. How to measure your respiratory rate
  43. How to safely go to your doctor during the COVID-19 pandemic
  44. How to take your temperature
  45. How to talk to your kids about COVID-19
  46. Loss of smell
  47. Mayo Clinic Minute: You're washing your hands all wrong
  48. Mayo Clinic Minute: How dirty are common surfaces?
  49. Multisystem inflammatory syndrome in children (MIS-C)
  50. Nausea and vomiting
  51. Neurosurgery during the COVID-19 pandemic
  52. Parenting and special needs during a pandemic
  53. Pregnancy and COVID-19
  54. Coronavirus infection by race
  55. Red eye
  56. Routine cancer screening during coronavirus (COVID-19) pandemic
  57. Safe outdoor activities during the COVID-19 pandemic
  58. Safety tips for returning to school during COVID-19
  59. Sex and COVID-19
  60. 呼吸短促
  61. Skin care tips during a pandemic
  62. Stay healthy during the COVID-19 (coronavirus) pandemic
  63. Stay on track with medications during a pandemic
  64. Telemedicine online doctor visits
  65. Teleworking during the coronavirus
  66. Thermometers: Understand the options
  67. Video: Travel safely for medical care during the COVID-19 pandemic
  68. Treating COVID-19 at home
  69. Unusual symptoms of coronavirus
  70. Watery eyes
  71. Fight coronavirus transmission at home
  72. Contact tracing and COVID-19: What is it and how does it work?
  73. What's causing my infant's diarrhea?