Your COVID-19 test is negative. What does that mean?

As Ontario moves forward with enhanced testing of asymptomatic individuals through a self-referral process, the burden will often fall on those getting tested to interpret their own results, rather than relying on health-care providers. While a negative test may seem reassuring, there are several caveats to be aware of to ensure that a proper response is undertaken.

How does a COVID-19 test work? The test detects the presence of viral genetic material (RNA) through a process called RT-PCR (real time polymerase chain reaction). After a swab is inserted through the nose into the back of the throat (nasopharynx), it is rubbed against the inside surface, in order to collect cells and virus. The sample goes to the lab, and is put through a reaction to determine if viral RNA is present. If there is no RNA in the sample, then the test is recorded as “negative.”

Who should be tested?

People with symptoms consistent with COVID-19 should get tested (use the provincial tool for an up-to-date list of symptoms). A negative test usually means that the symptoms are not attributable to COVID-19. However, particularly in those presenting with COVID-19 pneumonia, repeat testing or a sputum sample may be needed. This approach is largely limited to patients requiring hospitalization.

What does a negative result mean? A negative result, either while symptomatic or asymptomatic, could mean any of the following: a) You don’t have COVID-19 currently; b) You have COVID-19, but the test is a “false-negative.” While the test is very sensitive, a negative result can occur if a swab is done incorrectly, if there are issues with the equipment used to do the test, or the swab or liquid media used to transport the sample.

A negative result does NOT mean:

a) You did not have COVID-19 in the past, or will not have it any other point in the future. The result is only a snapshot of the day you had the test and nothing more;

b) You do not have to self-quarantine if you were exposed to COVID-19. The virus may take up to 14 days to incubate. A negative test simply means that, on the day of your test, you were not shedding the virus. It does not mean that you are clear of COVID-19 after a possible exposure. It does not preclude the need for the 14 days of quarantine after travel, or after a significant exposure to someone with COVID-19;

c) You do not have to adhere to physical distancing and hygiene measures. You are still at risk.

As testing becomes more widely available for asymptomatic individuals, the onus is on employers and the public to use these tests rationally. Testing is not a replacement for controls in workplaces to prevent the spread of COVID-19 such as physical distancing, hand hygiene, cough etiquette, staying home when sick and wearing a mask if needed. Likewise, it is not a reliable tool for preventing COVID-19 introduction to the workplace and, if interpreted incorrectly, can lead to a false sense of security and actually increase the risk of acquiring and spreading COVID-19.

As we expand testing, targeting of asymptomatic, high risk and exposed populations is an important tool to generate meaningful data and track the spread of COVID-19. Maximum benefit from this strategy requires awareness of the limitations of a negative result in order to guide decision-making for those who have been tested. Dr. Zain Chagla is an associate professor at McMaster University and infectious diseases consultant St. Joseph’s Healthcare. Dr. Abdu Sharkawy is an assistant professor of medicine at University of Toronto, division of infectious diseases University Health Network.