We’ve all felt uncertain at times during the COVID-19 pandemic. Do I have the coronavirus? Should I get tested? Do I need to quarantine?
Rapid coronavirus tests may offer comfort – and convenience – to some, but are the results accurate? We asked Micah Bhatti, M.D., Ph.D., if these tests are dependable and five other common questions related to rapid coronavirus tests.
How do rapid COVID-19 tests work?
There are two types of rapid COVID-19 tests that detect the coronavirus. One type is a sped-up, smaller version of the PCR tests. It’s also molecular-based, so it’s looking for genetic material from the virus in the mucus and infected cells in the sample from the patient. The sample is collected by inserting a cotton swab up the nose or running it along the inside of the cheek. The collected material is then added to a tube of fluid, and that’s what we’re testing in the lab.
The other style of rapid test looks for antigens of the virus, which are proteins on the surface of the virus. The mucus and cells are collected in the same way as a PCR test, but these tests may not require a lab to determine the results. These tests often come as flat card that contain a test strip. The test strip reacts with coronavirus antigens present in the patient’s mucus sample, and the strip typically changes color to indicate that the patient is positive.
Are rapid COVID-19 tests reliable?
To a certain degree, you’re sacrificing accuracy with speed. By their very nature, the antigen style tests aren’t as sensitive because they require a larger amount virus present to be positive.
They can be helpful in rapidly screening symptomatic individuals. They can also help to rapidly screen a large group of individuals during an outbreak in a resource-limited setting. Someone with a positive result by this style of test should be treated as infected with COVID-19, but a negative test is less reliable and should be confirmed by a more sensitive molecular assay.
The rapid, molecular-style tests can be reliable if a quality specimen is used and if the testing is conducted by properly trained individuals who are performing the test as intended by the manufacturer. This is the exact standard that we provide in the clinical laboratories at MD Anderson. With a sophisticated setup like ours, we’re able to detect the genetic material of the coronavirus, even when there’s only a small amount in the sample.
Are at-home rapid COVID-19 tests dependable?
While we're leaning more into rapid antigen tests and the government's making them available, the accuracy of the tests hasn’t changed. They're more accurate in symptomatic people than asymptomatic people.
When used a day or two into experiencing flu-like symptoms, a positive at-home antigen test can confirm a coronavirus infection. But a negative test result can’t rule it out. Antigen tests still carry the disclaimer that a negative result needs to be confirmed by a molecular test.
What types of COVID-19 tests does MD Anderson use?
At MD Anderson, we still rely on our in-house molecular, PCR-based test. We know it’s accurate and trustworthy because of our internal vetting process. If we used a rapid test with a patient who is symptomatic and the result was negative, we’d have to do another test. It’s just not efficient. Secondly, most people we test don’t have symptoms, and we know an antigen test isn’t sensitive enough to detect the coronavirus in that situation.
We test our patients prior to coming in for procedures to protect their health for two reasons. First, because cancer treatments can weaken the immune system, our patients and survivors are particularly vulnerable to coronavirus infection. Second, being positive for COVID-19, even if asymptomatic, could influence the success of cancer treatment, particularly with certain types of chemotherapy or cell-based therapies. If you have a COVID-19 infection brewing, it can lead to a higher risk of complications. To minimize that risk, we do a test ahead of time. And if it’s an emergent procedure, we have precautions in place to make it as safe as possible for everyone involved.
Patients being admitted to our hospital or being seen in our Acute Cancer Care Center may receive a rapid molecular, PCR-based test that has gone through the same internal assessment to ensure its reliability. The rapid test allows us to quickly isolate and treat patients who may be positive for the coronavirus infection. However, because of the volume of patients that we care for, we’re unable to offer this option to everyone.
If I’ve taken a rapid COVID-19 test, what do the results mean?
If you’re experiencing symptoms of COVID-19 and a rapid test result indicates you’re positive, you should take that as an indication you have the coronavirus. You should quarantine and contact your doctor.
However, if you have COVID-19 symptoms and a rapid test result is negative, you should still contact your doctor because to schedule a PCR test. Don’t be victim of a false sense of security with a false negative result from a rapid COVID-19 antigen test.