What are the tests for COVID-19?
What are the tests for COVID-19?
As the pandemic progresses more and more tests are coming in the market to tests for COVID-19 infection. It has created lot of confusion in public. Here I try to demystify the tests available.
What are the tests?
As COVID- 19 is a novel virus it is obvious that all these tests ae new and data regrading accuracy and other parameters were not available in the beginning.
Diagnostic tests for current infection
If you want to know if you are currently infected with the COVID-19 virus, there are two types of tests: molecular tests and antigen testing.
Molecular tests (also called PCR tests, viral RNA tests, nucleic acid tests)
How is it done? Nasal swabs, throat swabs, and tests of saliva or other bodily fluids.
Where can you get this test? At a hospital, in a laboratory and even mobile vans are available where you can get the tests done..
What does the test look for? Molecular tests look for genetic material that comes only from the virus.
How long does it take to get results? It depends on lab capacity. Results may be ready the same day, but usually take at least a day or two.
What is the accuracy? False negatives — that is, a test that says you don’t have the virus when you actually do have the virus — may occur. The reported rate of false negatives is as low as 2% and as high as 37%. The reported rate of false positives — that is, a test that says you have the virus when you actually do not — is 5% or lower.
Its important to remember that if test is negative there is no guarantee that you are not infected with COVID-19 in that case doctors may try to gather
A molecular test using a deep nasal swab is usually the best option, because it will have fewer false negative results than other diagnostic tests or samples from throat swabs or saliva. People who are in the hospital, though, may have other types of samples taken.
How is it done? A nasal or throat swab.
Where can you get these tests? At a hospital or in the lab.
What does the test look for? This test identifies protein fragments (antigens) from the virus.
How long does it take to get results? The technology involved is similar to a pregnancy test or a rapid strep test, with results available in minutes.
What about accuracy? The reported rate of false negative results is as high as 50%, which is why antigen tests are not favored by the FDA as a single test for active infection. However, because antigen testing is quicker, less expensive, and requires less complex technology to perform than molecular testing, some experts recommend repeated antigen testing as a reasonable strategy. According to one test manufacturer, the false positive rate of antigen testing is near zero.
Tests for past infection
Antibody tests (also called serologic testing)
How is it done? A sample of blood is taken.
Where can you get these tests? At a blood testing lab, or hospital.
What does the test look for? These blood tests identify antibodies that the body’s immune system has produced in response to the infection. While a serologic test cannot tell you if you have an infection now, it can accurately identify past infection.
How long does it take to get results? Results are usually available within a few days.
What about accuracy? Having an antibody test too early can lead to false-negative results. That’s because it takes a week or two after infection for your immune system to produce antibodies. The reported rate of false negatives is 20%. However, the range of false negatives is from 0% to 30?pending on the study, and when in the course of infection the test is performed.
Research suggests antibody levels may wane over just a few months. And while a positive antibody test proves you’ve been exposed to the virus, it’s not yet known whether such results indicate a lack of contagiousness or long-lasting, protective immunity.
The true accuracy of tests for COVID-19 is not known
Unfortunately, it’s not clear exactly how accurate any of these tests are. There are several reasons for this:
- We don’t have precise measures of accuracy for these tests — just some commonly quoted figures for false negatives or false positives, such as those reported above. False negative tests provide false reassurance, and could lead to delayed treatment and relaxed restrictions despite being contagious. False positives, which are much less likely, can cause unwarranted anxiety and require people to quarantine unnecessarily.
- How carefully a specimen is collected and stored may affect accuracy.
- A large and growing number of laboratories and companies offer these tests, so accuracy may vary. At the date of this posting, more than 170 molecular tests, two antigen tests, and 37 antibody tests are available.
- All of these tests are new because the virus is new. Without a long track record, assessments of accuracy can only be approximate.
- We don’t have a definitive “gold standard” test with which to compare them.
Getting a test for COVID-19 can be confusing because the options are rapidly changing and tests from many companies are being marketed. Despite the current limitations of testing, we’re lucky to have reasonably accurate tests available so early in the course of a newly identified virus. Imagine where we’d be if that was not the case.
Still, we need better tests and better access to them. And all tests should undergo rigorous vetting by independent agencies like ICMR in India or FDA in the US
as soon as possible. Lastly, widely available tests and short turnaround times for results are essential for effective contact tracing and getting this virus under control.
Dr. Rakesh Rai. MS, FRCS, MD, ASTS Fellow (USA)