There is a lot of confusion about Coronavirus testing - should I get tested? When? How often? Which test? What do the results mean?
One reason for so many questions is that we still don't know very much about COVID-19, although we're learning new information every day. So I've tried to explain testing and what it does (AND DOESN'T) tell us.
TYPE OF TEST:
Virus Test - The test for
active
Coronavirus infection is done by
PCR (polymerase chain reaction) which picks up even very tiny amounts of viral RNA. This is usually done by
deep nasal swab. Yes, this can be uncomfortable, but that's where the virus lives in large amounts, so it is the best place to sample. Throat swabs are less sensitive so you might get a negative result but still be infected.
- Rapid test - Results within 15-30 minutes. This requires an expensive machine to run, so it's often only available in ER or hospitals.
- Standard test - Is done by most labs, turnaround is usually 2-5 days
Antibody test - this test tells is if we've been infected
in the past. These antibodies develop about 4 weeks after the acute infection. This test requires a routine blood draw and turnaround time is about 1-2 days.
HOW GOOD IS THE TEST:
We've heard a lot about various tests with some being better than others. The FDA has given Emergency Use Authorization to a number of tests and
click here for a good explanation of their findings. All of the tests they've "approved" are performing reasonably well, so I've personally decided
not to get lost in this discussion (sensitivity, specificity, positive predictive value, negative predictive value, etc).
WHAT DO THE RESULTS MEAN
:
For this discussion, I'm assuming the test is accurate. But remember that no test is always 100% accurate.
Virus test (nasal swab):
- a positive test means there is virus RNA in your body - you are actively infected, even if you don't have symptoms. You are infectious to other people and should self quarantine. There is a caveat here - people who get infected with COVID-19 can remain positive on this test for up to 12 weeks. Since we do not believe people are infectious this long, it may be that the test is picking up dead virus. But this remains an area of significant uncertainty.
- a negative test means there is no virus RNA present - you are not actively infected. You are not infectious
Antibody test (blood test):
- A positive test means you've been infected with Coronavirus at some point in the past. This is very helpful to Public Health professionals to know what percentage of the population has been infected and how close we are to "herd immunity". It is less helpful for a specific individual and questions remain:
- it doesn't tell us when you were infected.
- We do not know how long these antibody tests remain positive - a few months, a few years or forever?
- We do not know if these antibodies protect us from getting infected again. With some viruses (e.g. cold viruses), antibodies protect us for a short while, but we can get infected again and again. With some viruses (e.g. chicken pox, measles) antibodies protect us and we only get infected once in a lifetime. And with other viruses (e.g. herpes, HIV), having antibodies doesn't help at all - we remain chronically infected.
- A negative test means you've not been infected with Coronavirus in the past. One caveat: If you're recently infected with Coronavirus, the antibody test will not become positive for about 4 weeks.
WHEN TO TEST:
With symptoms
- Always test if you have symptoms suggestive of Coronavirus.
After an exposure
- Not everyone gets infected even if exposed. But when (and if) to test is an
area of debate
. The incubation period of Coronavirus is 2-14 days. If you test negative on day 2, unfortunately you can still turn positive on day 3, 4, 5 up to day 14. So regardless of the results, you should self isolate for 14 days. One recommendation is to test on day 14 - if negative you can safely return to life.
Before visiting a high risk person
- Ideally get a rapid viral test right before you're planned visit. A negative result means you can visit Grandma without concern you'll spread it to her. This is limited by the availability of the rapid test (see "where to get tested" below). If you are planning on visiting Grandma for a week, however, you'll need to test every day which is often not feasible.
WHERE TO GET TESTED:
- I offer standard virus and antibody testing in my office. I do not have rapid virus testing.
- County testing sites can be found here. These sites are free and some require an appointment.
- Scripps is only testing patients with symptoms. If you are a Scripps patient, Call the Scripps Nurse line (888-261-8431) to get scheduled. They offer standard virus testing, they are not doing rapid virus testing.
- Many CVS locations offer standard virus testing with 2-4 day turnaround. Cost is usually covered by insurance. Register in advance at CVS.com
- CovidClinic.org in downtown San Diego offers rapid virus testing and antibody testing for about $150
- QuestDirect allows people to request an antibody test and pay for it online ($130). An appointment is then made for a blood draw at a Quest lab.
At Home testing - this is a rapidly expanding area with many unknowns currently. I will provide more information in the next newsletter.
