Testing, testing: The key to controlling coronavirus spread
The difference between swabs, point-of-care blood pricks and antibody tests
Widespread testing for the coronavirus is considered a key part of the pandemic response, both for diagnosing infections and, potentially, to ease lockdowns.
In Canada, provinces initially limited diagnostic tests for COVID-19 to health-care workers who were directly caring for patients, for people with severe symptoms and for those who work with vulnerable groups.
Backlogs have cleared, but testing is mostly still targeted — instead of the wider, ramped-up testing that infectious disease physicians are calling for to control the spread.
Here's a primer on different types of testing, and their pros and cons:
Swabs
Nose or throat swabs test for the presence of genetic material from the coronavirus. They aid in diagnosis and are also important for the detective work of tracing contacts — those who may have been exposed to an infected person, such as family members, health-care workers or nearby travellers
The swabs are typically inserted into a patient's nose and then sealed into a tube with growth medium to support the virus until it can get to the lab.
WATCH | What it's like to have a nasal swab:
The sample needs to be collected carefully from the correct area. It's estimated that errors can occur about eight to 10 per cent of the time, which contributes to false negatives.
Labs also need specialized equipment and skilled staff.
Provincial lab officials say the amount of virus in the upper respiratory tract seems to peak in the first week of symptoms and could fall too low to be detected later.
Despite the drawbacks, swabs are the gold standard for detecting a coronavirus infection.
Health Canada says only diagnostic tests that it authorizes can be imported or sold in this country, based on a review of evidence indicating they will provide accurate and reliable results.
There are no legitimate "home test kits" available in Canada.
Office-based tests
"Point-of-care" diagnostic tests use a blood prick sample, rather than a nasal swab. They can be done while a patient waits at a doctor's office, clinic or hospital, with results in under an hour.
But doctors and scientists still need to determine their accuracy in the real world, as opposed to under the ideal conditions of the testmaker's lab.
Diagnostic tests don't provide information about if someone's been previously exposed to the virus or has successfully mounted an immune response.
Blood tests for antibodies
That's where antibody or serology tests could come in. Instead of searching for the virus itself, these search for proteins in the blood called antibodies. Your body produces antibodies weeks after successfully fighting off an infection.
In Canada, antibody tests for COVID-19 are just a research tool and aren't available to the public.
Dr. Anthony Fauci, who heads the U.S. National Institute of Allergy and Infectious Diseases, has said it's a "reasonable assumption" that, if you have antibodies, you will be protected from another infection.
But scientists still need to test that assumption and find out:
- How accurate serology tests are.
- What antibody levels are needed for immunity?
- How long the immunity lasts.
Researchers hope to use antibody tests to learn how widely the coronavirus has spread and to nail down how deadly it is.
Experts say serology tests won't tell you how many antibodies your immune system has made in response to COVID-19. That's important because immunity often depends on having a high concentration of antibodies.
Health Canada said officials are being vigilant to ensure that serological testing is used appropriately, in conjunction with other laboratory tests.
On May 12, Health Canada authorized the first COVID-19 serological test for use in Canadian labs.
With files from CBC's Christine Birak, Amina Zafar and The Associated Press
