Tests for COVID-19: What’s the Difference Between Them?

June 15, 2020

The COVID-19 pandemic, tests, treatments, and outlook, continue to be front and center in the news, along with other urgent issues taking place across the country. Viral sepsis is the number one complication related to COVID-19, so the need to find a way to detect and manage the infection is urgent. Testing has evolved, but much work still needs to be done.

At the start of the pandemic, researchers developed swab tests to determine if you had the infection. As of June 12, 2020, there have been over 23 million tests reported to the Centers for Disease Control and Prevention (CDC), almost 2,500,000 were positive, which is about 11%. Now, scientists are working on antibody tests. These determine if you have been exposed to the infection at some time, even if you never had or no longer have symptoms.

COVID-19 Diagnostic Testing

Diagnostic testing for COVID-19 is easier to get now, after a slow roll-out earlier in the pandemic. Diagnostic tests diagnose or rule out certain conditions. The CDC offers guidelines regarding testing, but each state sets its own policies. Call your local health authority who should direct you to the right information for your state.

Most places will test you if you have/are:

  • Symptoms (fever, dry cough, loss of taste or smell, tight chest, difficulty breathing are a few)
  • In close contact with someone who is COVID-positive
  • Identified through contact tracing as at risk for contracting COVID-19
  • In a living situation that is crowded, with no possibility of physical distancing
  • A healthcare worker
  • Hospitalized

Should Asymptomatic People Be Tested?

At first, people who were asymptomatic, had no symptoms, were not tested for the novel coronavirus that causes COVID-19. However, more states are now open to testing the asymptomatic group. “The evidence we have right now shows that the virus can be transmitted from people who either never develop symptoms or who are going to but just haven’t yet,” Steven Q. Simpson, MD, explained. Dr. Simpson is a professor of medicine at the University of Kansas in the Division of Pulmonary, Critical Care, and Sleep Medicine, and Sepsis Alliance Chief Medical Officer. Doctors and researchers can get a more complete picture of the virus and how it’s transmitted through testing those who don’t have symptoms . “While the test may not help you, individually (though it might, if you are just pre-symptomatic), the information gathered will be of use to the national effort to fight the virus,” Dr. Simpson added.

Swab Testing Procedure

The most common diagnostic test for COVID-19 is a swab test using secretions taken through your nose. There are now also some saliva tests. A healthcare worker inserts a long handled swab deep into your nasal passage. “The virus is present throughout the respiratory tract, including in the nose, but the concentration of viral particles becomes higher the deeper into the respiratory tract one looks,” Dr. Simpson said. “The swab needs to go deep into the nasal passage to make sure that the concentration of virus allows the test its best chance of detection.”

The sample goes to a laboratory where laboratory technicians check for the virus. This is a nucleic acid amplification test, or a genetic test, an RNA test, or a PCR test.

There are some points to remember about the swab test:

  • A negative test only indicates that you did not have the virus at that time. You can still contract the virus after the test and test positive if you have another swab later on.
  • It is possible to have a false negative test. If you have symptoms of the viral infection or you have been in contact with someone you know is COVID-positive, you should take extra precautions, despite the test results. If your test was negative, you don’t have symptoms and you have not been in contact with someone who does have the infection, you should still maintain the safety rules (distancing, hand washing, and masks) to reduce the risk of becoming infected later.
  • A test may also be inconclusive, meaning the lab cannot tell either way if you have the infection. You may need a repeat test. This could happen if the person taking the swab doesn’t go far enough into the nasal passage or not enough secretions were on the swab.

Antibody Testing

You may have heard people referring to antibody testing in relation to COVID-19. This is not a diagnostic test. It is one that detects if you have been exposed COVID-19 at some point, past the actual exposure. According to the CDC, it takes between one and three weeks after infection to develop antibodies to this coronavirus.

Germs that cause infections are antigens. Antibodies fight antigens. Once an infection clears up, you might have lasting antibodies that protect you from becoming ill with that same virus if exposed to it again. Some antibodies help to outright kill the virus or prevent it from reproducing and spreading to more cells. Other antibodies recognize a virus is an invader, but they attack parts of the virus that are less vital to its survival.

Reasons for antibody testing:

“There are two reasons to take an antibody test [for COVID-19],” Dr. Simpson said. “First, it tells whether you have had the disease. That is important information for public health physicians and officials. The second reason is to determine whether you have immunity.”

When developing an assay (test), scientists look for the antibodies that kill the virus. “However, in the rush to develop testing during this outbreak, not all of the antibody tests were well enough studied to know whether they detect killing antibodies or other antibodies,” Dr. Simpson explained. “Some of the antibody tests do, in fact, test for the killing antibodies. The problem is that a person usually doesn’t know what test their laboratory is using.” In other words, the antibody tests are good at telling whether you have had the disease but not all tests can tell if you have reasonable immunity.

“The only way to know the difference in tests is to ask the testing facility whether they are using an antibody test that assesses “neutralizing” antibodies. With time, we expect that most antibody tests will be for neutralizing antibodies. Again, though, for public health purposes, it is useful to know who has had the virus, so that is a good reason to have a test,” Dr. Simpson said.

Antibody tests require blood samples. They do not replace swab testing.

Scientists don’t know yet if people who had COVID-19 do become immune to the virus and can’t get it again. And if they are immune, scientists don’t know how long such an immunity might last. There are still many questions. However, scientists need these tests to learn more about the virus and how it affects survivors.

To learn more about Sepsis Alliance coverage of the COVID-19 pandemic, visit the Coronavirus (COVID-19) Resource Page.