As COVID-19 tests become more widely available, some confusion has arisen over which test to get: the viral diagnostic test or the antibody version.
KERA's Sam Baker sought some answers from Dr. Joseph Chang, Chief Medical Officer at Parkland Hospital and Health System.
Viral Test vs. Antibody Test
The viral test takes active virus on your mucus membranes and actually amplifies it in a lab — so we actually detecting the virus itself. The antibody test, however, a blood test, [shows] the reaction of the body to the virus.
When Should You Get Either Test?
When you are sick, the viral test is the one to get. The antibody test can take weeks for the body to make enough antibodies in the blood that you can actually see the result in the blood. So, getting the antibody test doesn’t actually tell you if you have it, because it's going to take another few weeks for that to show up.
Reliability Of Both Tests
Many different companies have come out with their own versions of the test. As you can imagine with different brands of anything, the sensitivity of those tests can vary according to the companies that make it. At Parkland Hospital, we know from published studies that our test is over 98% sensitive for detecting the disease, but that's not necessarily true for every test.
Does A Negative Test Result Mean You Won't Get Sick Later?
For the diagnostic test, if you have a negative test right now, what that means is that you have over 98% chance that you do not have the virus in your body, at least right now, to a detectable level.
However, remember sometimes the virus simply has not replicated to a high enough level in the body to be detected yet. So it could be that today you're negative, but in three days you would actually be positive. A lot depends on timing, but if you do have symptoms and you have a negative test, then it likely means you don't have the actual disease.
When Should You Get Tested?
When you feel like you have respiratory symptoms, when you feel ill, have a fever, or any of those kinds of things, that would be the time where you would really have the best shot of getting results that are meaningful.
Should You Call Your Doctor First?
It's much more advisable to go to a licensed professional first to determine if a test is even necessary. And second, they could send you to a place where you can get a reliable test.
One More Thing…
With the state opening up all of the areas that had been closed off for shelter-in-place, it’s really important to do two things:
- Washing your hands and using hand hygiene gels goes a long way in stopping the spread of all viral illness.
- As you're walking around, outside, wear your mask. Until we get adequate treatments and or vaccines for this issue, the only thing we can do is prevent transmission.
Answers have been edited for clarity and brevity.
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