Since COVID-19 began several months ago, counties and states have reported the number of new cases every day. These numbers help public health officials provide recommendations for how your community can limit the spread of the virus. If the number of COVID-19 cases in your area is high and someone in your family is showing signs of COVID-19, you may want to get a test. But which test is the right one? What is an antigen test or “rapid test”? What is an antibody test? What does “PCR” mean? How are the tests done? When will I get my results? How accurate are they? The following information may be helpful to answer these common questions.
What is a rapid test? (also called an antigen test)
An antigen is a structure that is found on the surface of a virus or bacteria; it is specific to that type of illness. A rapid test can identify an active infection by detecting an antigen of a virus or bacteria from a mucus or saliva sample taken with a nasal or mouth/throat swab. Your child may have had an antigen test at some point to identify the flu or Strep infection. Rapid tests are very convenient for a fast diagnosis and the results usually come back within the hour, most results are ready within twenty minutes.
How reliable are rapid tests?
Rapid tests are reliable when the result comes back as positive. However, things get tricky when the result is negative. A negative result may mean that your child does not have that specific infection, and their symptoms are coming from somewhere else. For example, a rapid test for a specific bacterial strep infection would not detect a virus or allergy that is causing their sore throat. A negative result can also happen if the swab doesn’t get a strong sample. This can happen due to user error or a squirming patient (those tests are not comfortable!). Lastly, if the test is done too early, there may not be enough of the antigen present to detect the infection.
A negative rapid test result may require a follow-up test that is more accurate, such as a PCR test. This test can confirm a true negative (your child does NOT have the virus) or catch a false negative (your child has the virus, but that convenient rapid test wasn’t sensitive enough to pick it up).
What is the PCR (Polymerase Chain Reaction) test? (also called a molecular test)
PCR testing is used in labs to quickly duplicate the DNA or genetic material of a virus or bacteria in order to make a sample to study and identify. PCR tests have been used before COVID-19 to identify infections such as influenza, RSV, whooping cough, and tuberculosis. They are completed by taking a small sample of mucus or saliva with a swab in the nose or mouth.
How reliable are PCR tests?
The PCR test is considered the most accurate test for detecting an active COVID-19 infection. The PCR test is more accurate than an antigen test because it looks for very specific sequences or code combinations of the genetic material (DNA) instead of proteins. It can take a few days or a little over a week to get the results, depending on testing capacity. It may take even longer if your local health department or labs are trying to process a large number of tests. PCR tests are less convenient than rapid tests, but if the test result is negative, it’s unlikely another test is needed.
What is an antibody?
If an antigen is present in the body, it will trigger the immune system to react by activating a complex response in which the body deploys many types of cells, chemicals, and proteins. The immune system will produce a protein called an antibody that acts as a scout for the rest of the troops in the immune system. It sticks to the invader, sounds the alarm, and activates the troops of the immune system by sending out different chemical signals. Then, the antibody memorizes the identity of that invader and stores it in the immune system’s memory in case it encounters the invader again. It can take days to weeks for your body to make antibodies, so there are some limitations to tests that detect antibodies.
What is an antibody test?
An antibody test is usually a blood test that detects an antibody for a specific type of infection. A positive test result means the immune system responded to exposure to infection by creating an antibody. A positive test result means a past infection, but not necessarily an active one. A negative test result could mean no exposure to the infection, or it may be too soon for the test to detect the antibodies.
How reliable is the antibody test?
COVID-19 is unlike anything the world has seen before, and there are new findings and discoveries about it daily. This means there is not enough research or data to tell us if the antibody tests are reliable. The CDC and the FDA currently recommend the PCR test as the most reliable test to date, followed by the rapid antigen test.
Below you will find some additional helpful information from the CDC, FDA, and the American Academy of Pediatrics (AAP). To learn more about this topic, and other topics discussed in our blogs, join our weekly webinars. Register here.
National Institutes of Health Allergy or Flu
Centers for Disease Control and Flu Symptoms
Centers for Disease Control and Prevention COVID-19 and Season Allergies
AAP (Healthy Children) Allergies
Centers for Disease Control and Prevention: Similarities and Differences between Flu and COVID-19
Emerson Hospital: Allergies or COVID-19
Centers for Disease Control and Prevention: Overlap of COVID-19 symptoms with seasonal allergy symptoms