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Types of tests

Viral tests can tell you if you have COVID-19 right now and are potentially infectious to others.

Last updated: September 17, 2021

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Viral tests

A viral test will tell you if you have COVID-19 right now and are potentially infectious to others.  Viral tests look for the presence of genetic material from the actual virus and require a sample to be taken from your nose or throat. Please see our When to get a test page to help you decide if you need a test. 

PCR tests

COVID-19 tests use polymerase chain reaction (PCR) technology to look for viral genetic material. Viruses contain genes or genetical material. PCR COVID-19 tests work by measuring how much genetic material, if any, is in someone’s sample. 

SARS-CoV-2 is the coronavirus that causes COVID-19. PCR tests detect one to three genes specific to SARS-CoV-2. COVID-19 PCR tests only detect SARS-CoV-2, not other types of coronaviruses.  PCR tests are considered the gold standard of SARS-CoV-2 testing. 

The following video shows how the viral testing process works.

 


  1. Sample Collection: A sample is collected from either a nasal swab or saliva from a mouth rinse and gargle. 
  2. Extraction: Any SARS-CoV-2 genetic material in the sample is isolated. 
  3. Conversion of RNA to DNA: SARS-CoV-2 has genes or genetic material in the form of RNA. PCR tests detect DNA, so the RNA is converted to DNA using heat and enzymes. 
  4. Amplification: Since the sample is small, there won’t be enough genetic material to test yet. The genetic material needs to be amplified. This creates millions of copies of the genetic material.
  5. Detection: Once amplified, the PCR test can detect if SARS-CoV-2 genetic material is present. 
 
There are currently 2 main ways to perform viral PCR tests for COVID-19 in BC:

  • Nasal Swab (also know as the nasopharyngeal swap or NP swab): The nasal or nose swab is used for younger children, people with a strong gag reflex, or those who may not be able to follow the swish, gargle and spit instructions. There are no special preparations needed for this test. 

  • Mouth Rinse and Gargle: Mouth rinse and gargle sample collection is available to both adults and school-aged children at community collection centres. Carefully review the mouth rinse and gargle instructions on this page before you go for testing.
Cycle threshold values (Ct values) are the number of cycles or rounds of amplification needed to detect SARS-CoV-2. 

When there is less virus in the sample, more rounds of amplification are needed which results in a high Ct value. When there is more virus in the sample, fewer rounds of amplification are needed which results in a low Ct value

Ct values don’t tell us much in themselves without proper context. Ct values depend on many factors, examples include:
  • Where the sample is collected from. For example, a nasal swab or saliva using the mouth rinse and gargle method
  • When you get tested after exposure to COVID-19 (see image below)
  • Sample quality
  • Sample storage
  • Sample transportation time. 

The blue line in this image shows how the amount of SARS-CoV-2 viral material in your body can change over time. When there’s a low amount of virus in your body, the Ct value is high. This means more amplifications are needed to detect the virus. 

 
Ct value cut-offs determine if a sample is positive or negative. Cut-offs vary by the type of PCR test. Typically, a threshold of about 35 cycles is used to determine if someone has COVID-19. This means if there is no virus detected after 35 cycles, the sample is considered negative. 

Laboratories and manufacturers set cut-off Ct values when they develop the test. Many PCR test technologies report whether the virus was detected or not, not the exact Ct value. 

There are currently ten different PCR tests used in BC. You can find out more about each test on the manufacturer webpages:

False positive test results mean someone tests positive when they do not have COVID-19.


False negative test results mean someone tests negative when they do have COVID-19.


  • Both false positives and false negatives are rare when the sample is taken correctly and at the correct stage of infection. 
  • If COVID-19 case rates are low but many people are still getting tested, false positive are more likely to happen.
  • Although rare, false negatives can happen when you don’t yet have enough virus in your body to be detected by a PCR test. This means you could have a negative COVID-19 test result, but show symptoms later. Complete any self-isolation when directed, even if you have a negative PCR test result.

Point-of-care tests

A point-of-care (POC) test is a tool that can be used to rapidly screen people for COVID-19 in certain settings to help reduce the chances of outbreaks and control the spread of COVID-19. Results are usually ready in less than 20 minutes. They can be less accurate than the standard COVID-19 test, called a PCR (polymerase chain reaction) test. This means that POC tests have a higher chance of false results compared to PCR tests.

Publicly funded POC tests are used as part of BC’s Rapid Point of Care Testing Strategy. Learn about the Rapid Point of Care Screening program.

In most cases, POC tests are only recommended for screening people with no symptoms and who are not self-isolating. If you have symptoms, please use the self-assessment tool to determine if you need a PCR test.

Because POC tests are less accurate than the standard COVID-19 PCR test, POC test results are considered “presumptive.” This means that the results have not been proven by a laboratory test. 

There are three possible results from POC tests:

  1. Positive: You will need to self-isolate and go for a standard COVID-19 PCR test to confirm the result. It is important to monitor how you feel. If you develop symptoms such as struggling to breathe, chest pain, being unable to drink, feeling very sick or confused, or any other symptoms that concern you, seek urgent medical care. You should continue to seek care for other medical conditions as needed, even if they are not related to COVID-19.

  2. Negative: You are still expected to follow standard public health recommendations. If you are self-isolating, you should continue until the end date provided by public health.

  3. Invalid: This means that the test was not performed correctly or the test kit was defective. You may be asked, or want, to take another POC test.

This document has information that will let you know what to expect and what you need to do if you get rapid testing:


Handout: Rapid point-of-care screening

Sample Collection for PCR tests

Nasal swab

The nasal or nasopharyngeal (NP) swab test involves inserting an approximately 10 cm long, very thin probe through the patient’s nostril and into the back of the nasal cavity. The test takes about 5 seconds to complete.

 


Mouth Rinse and Gargle testing 

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Prepare for a test

Practice the swish, gargle and spit technique with salty water at home before going for a test. Do not swallow the salty water or talk while you practice. 


How to make salty water for practice

Mix ½ teaspoon (2.5mL) of salt in 1 cup of warm water to dissolve and cool to room temperature. 


See the instructions on how to make saline at home to practice.


If you live in an area with a Boil Water Advisory, boil water for at least one minute and then add the salt and allow to cool to make the salt water. If you live in an area with a Do Not Consume or Do Not Use Advisory, use bottled water to make the salty water solution for practicing.


Mouth rinse and gargle COVID-19 test for children

 

Mouth rinse and gargle COVID-19 test for adults

 


ASL: Mouth rinse and gargle COVID-19 test for younger children

 


ASL: Mouth rinse and gargle COVID-19 test for older children and adults
 


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