COVID-19 false negative tests: Challenges, implications & ways to tackle it

There is broad consensus on the need for extensive testing to tackle the burden of COVID-19. The bigger issue that we are currently dealing with is the accuracy of tests. Therefore, understanding the accuracy aspect of testing kits is significant. Diagnostic tests (typically involving a nasopharyngeal swab) can be inaccurate in two ways. A false-positive result erroneously labels a person infected, with consequences including unnecessary quarantine and contact tracing. False-negative results are more consequential because infected persons — who might be asymptomatic — may not be isolated and can in fact infect others!

So, how can we tackle this issue? 

Typically, patients who are at a high-risk of virus exposure should be treated as if they have been infected, especially if the symptoms are consistent with COVID-19; this means communicating with patients about the tests’ shortcomings. If a swab misses collecting cells infected with the virus, or if virus levels are very low during the infection, some RT-PCR tests may produce negative results. Since the antigen tests return relatively rapid results, they have been widely used among high-risk populations such as nursing home residents, hospitalized patients, and healthcare workers. Previous studies have shown or suggested false negatives in these populations.

 Understanding the false-negative for false positives

 Researchers projected that patients tested for SARS-CoV-2 within four days after the symptoms started showing, were 67% more likely to test negative, even if they did have the virus. The test is best performed eight days after infection (on an average – three days after symptom onset), but even then there was a false negative rate. Therefore, the sooner people are accurately tested and isolated from others, the better the control over the spread of the virus, researchers say.

While both false negatives and false positives are undesirable, false negatives run the risk of increasing community transmission – as people believe they are infection-free. This can occur whether or not people have symptoms.

Significance of the PCR and the antibody test for COVID

Several recent studies have highlighted a significant rate of false negatives, particularly if the test is administered soon after exposure to the virus. In these cases, viral material may not be captured through testing as the virus content in the person may not enough to be picked up. It is also possible that poor testing techniques can miss any virus that is there. The PCR test for COVID-19 works by detecting genetic material from SARS-CoV-2, the virus that causes COVID-19. If a person has tested positive for COVID-19, one can be sure that he/ she has been infected. The antigen test for COVID-19 is also accurate, which seldom gives a false positive.

To summarize, the time of collection of the sample, viral load of the patient, the method of collection, transportation of the sample, and the reagent used while testing, can all alter the results of the reports and can cause false negative or false positive reports. It is important to connect with your doctor as soon as you come in contact, or start showing symptoms, they will guide you in terms of testing and treatment.

About Author: Dr Farah Ingale, Director-Internal Medicine, Hiranandani Hospital Vashi-a Fortis Network Hospital. With over three decades of work experience, Dr Ingale is one of the most experienced doctors in the field. She strongly believes in promoting health awareness and a healthy lifestyle. She has published several papers about diabetes, renal disorders, ARF, immunomodulation, renal sepsis, kidney function, and metabolism.