Amidst all the testing for COVID-19 that’s been taking place globally, there have been cases when test results came out with false negative outcomes. Inasmuch as test results are critical to efforts in battling the spread of the novel coronavirus, researchers at the Johns Hopkins University (JHU) conducted a study to find out why false negative results happen, even if patients already show symptoms of infection.
In the report published last May 13 in the Annals of Internal Medicine by JHU School of Medicine researchers, it was learned that while testing is important, taking a test for COVID-19 at the early stage of the coronavirus’ incubation will likely yield a false negative result. If the symptoms persist and worsen, another test taken will subsequently prove whether the symptoms are indeed caused by COVID-19 infection. The question however is when should the test be taken?
Lauren Kucirka, M.D., Ph.D., M.Sc., a resident obstetrics and gynecology doctor at Johns Hopkins Medicine that it is important for everyone to know that a negative test does not guarantee a non-infected condition. That being the case, negative test results coming from individuals considered as high risks (elderly people aged 60 and above, and with existing medical conditions) should continue with treatments as if they are COVID-19 positive.
Dr. Kucirka explained that false negatives happen if in a Real-Time Reverse Transcription Polymerase Chain Reaction (rRT-PCR) a swab fails to collect virus-infected cells; or if the virus levels of infection in a person is still very low, there’s always a chance for the rRT-PCR test to yield negative results.
rRT-PCR are widely used among high-risk populations housed in nursing home and among hospitalized patients, as well as in health care workers. These are the specific areas and people who have shown false negative results.
What Stage is Too Early for Testing?
Johns Hopkins Medicine researchers reviewed and analyzed RT-PCR test data from 7 previous studies, covering 1,330 respiratory swab samples from different subjects including individual who have been identified by way of via contact tracing and those undergoing treatment as outpatients.
The analysis showed that those tested for the COVID-19 virus researchers estimated that those tested within four days after infection, had 67% chance of yielding negative results. Yet when the average person who tested negative begin showing symptoms of the virus, chances of false-negative lowers at 38%.
Finally, John Hopkins researchers arrived at a conclusion that the best time to perform a test is on the 8th day after infection or exposure. At that stage, the chances of producing a false negative result has gone down to 20%. This means that at that point, one out of every five patients who show signs of having the virus will actually show a negative result.