How is the COVID-19 antibody test different from a diagnostic test?

Q: I’ve heard about the new antibody test for COVID-19. What is an antibody test? Is it the same as the test to diagnose COVID-19?

Answer: With all the news about the Coronavirus Disease 2019 (COVID-19) test published in the news, it’s no wonder that there’s confusion about the tests and their differences. An antibody test will determine if you have COVID-19 in the past and you now have antibodies to the virus. A test to diagnose COVID-19 will determine if you currently have the disease. Here’s what you need to know about testing:

When are antibody tests done and why is it important?

Antibody tests, also called serologic tests, are done after complete recovery from COVID-19. Eligibility depends on the availability of the test. Medical professionals usually take a blood sample by pricking a finger or drawing blood from a vein in an arm. The sample is then tested to determine if it has developed antibodies to the virus. The immune system produces these antibodies — important proteins in fighting and clearing the virus.

If tests show that the antibody is present, it is likely that COVID-19 was infected at some point in the past. It also means being immune. However, the World Health Organization warns that there is a lack of evidence as to whether having antibodies means being protected from reinfection with COVID-19. The level of immunity and duration of immunity are still unknown. Ongoing research will eventually reveal more data on this.

The timing and type of antibody test affects accuracy. If you’re testing early in your infection, you may need to wait a few days before your test, because your body may still have an increased immune response but your test may not detect antibodies. Also, although the US Food and Drug Administration (FDA) has approved and validated certain antibody tests, many tests of questionable accuracy are currently on the market.

Another benefit of accurate antibody testing is that a person who recovers from COVID-19 may be able to donate plasma, which is part of their blood. This plasma can be used to treat severely ill people and increase their ability to fight the virus. The doctor will call the plasma for this recovery period. In the United States, the COVID-19 Extended Access Program has recruited participants for this promising therapeutic study and has already used it ly in some severe cases.

What tests are used to diagnose COVID-19?

The FDA has approved two types of tests to diagnose COVID-19, a molecular test and an antigen test.

• Molecular test. This test uses a lab method called the polymerase chain reaction (PCR) to detect the genetic material of the virus. Healthcare workers, also called PCR tests, collect fluid from swabs of the nose or throat, or saliva. Results in minutes when analyzed on-site and 1-2 days when sent to an external lab. When properly performed by healthcare professionals, molecular tests are considered to be very accurate, but rapid tests seem to miss some cases. The FDA has also approved certain COVID-19 home testing kits. It is only available with the approval of your doctor. Nasal swab kit and saliva kit. Samples will be mailed to the lab for testing. The FDA warns consumers not to buy unapproved home testing machines because they may be unapproved and potentially unsafe.
• Antigen test. This new COVID-19 test detects specific proteins that are part of the virus. A body fluid sample is taken using a nasal or throat swab and the antigen test provides results in minutes. Because these tests are faster and less expensive than molecular tests, some experts find it more practical to use an antigen test for more people. Positive antigen test results are considered highly accurate, but false negative results are more likely. That is, you may have a virus, but you have a negative antigen test result. Therefore, antigen testing is not as sensitive as molecular testing. In some situations, your doctor may recommend a molecular test to confirm a negative antigen test result.

What if I am interested in the COVID-19 diagnostic test or antibody test?

Please contact your doctor or other health care professional to discuss your situation and whether you need a COVID-19 diagnostic test or an antibody test. Before taking the COVID-19 test directly, contact your doctor to discuss your situation and explain your symptoms.

Generally, at this time, most doctors recommend tests to diagnose COVID-19 only if they have symptoms or have contacted someone with COVID-19. Complete recovery from COVID-19 is required to undergo antibody testing. However, in a limited number of communities, people who did not have COVID-19 symptoms were included in the test. Some have had positive results. So, at some point you may have been infected with the COVID-19 virus.

Access to either test depends on where you live, the availability of the test, and whether you are considered eligible. Collaboration is underway in the United States to make more tests available. The national goal is to test more people as more tests become available.

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

As more and more COVID-19 diagnostic tests become available, those who test positive and are symptomatic will receive faster care. To prevent the spread of the virus, you can track your contacts and start self-separation or quarantine faster.

However, there is no 100% accurate COVID-19 test. Although it is negative, it can actually become infected (false negative result). Therefore, it is important to continue to adhere to the COVID-19 guidelines from the Centers for Disease Control and Prevention, such as social distance, until further notice.

As accurate antibody tests become widely available, the results show how many people have recovered, including those who have COVID-19 and are asymptomatic. This helps determine who is immune. Contact tracking can also help you assess who else is at risk of infection and how far your illness is. All of this data helps improve strategies to control the COVID-19 pandemic.