Boland: Understanding the different types of COVID-19 tests

Over the last six months, the world’s scientists and experts have discovered and proven unique methods for identifying the coronavirus.

As science advances and becomes widespread, you may have a hard time following along with the latest tests and methodologies. You aren’t alone.

We asked Brian Mochon, PhD, a clinical microbiologist and system medical director at Sonora Quest Laboratories/Laboratory Sciences of Arizona for infectious disease testing, to provide his insight on the unique sample collecting strategies associated with COVID-19 testing.

He listed three ways to reach a diagnosis — throat swabs, nasal swabs and nasopharyngeal swabs. Dr. Mochon also discussed other alternative collection methods such as the use of saliva and the pooling of patient samples.

Swab collection

You’ve probably heard a few friends describe their experiences receiving a nasal swab. Some friends may go on about some discomfort while others dismissively say it was no big deal.

They’re both telling the truth.

“These samples can be collected from varying depths of the nose,” said Dr. Mochon. “Some swabs are designed to collect samples from the nasal walls of your nostril while others are collected from deeper in your nasal cavity (i.e., the nasopharynx).

Samples can also be collected from the back of throat, otherwise known as an oropharyngeal (OP) swab. All swabs are looking for the same thing — respiratory secretions and infected cells.”

So why isn’t everyone just choosing the most comfortable method? Dr. Mochon explained that “samples pulled from deeper in the nasopharynx have proven to have a higher viral concentration or titer. In other words, you are more likely to obtain a more accurate diagnosis when sampling with the nasopharyngeal (NP) swabs than you are with a nasal or throat swab.”

For this reason, the nasopharyngeal swab has been the standard for reliable testing.

“Of course, there is still a place for collecting samples from the nose or the throat,” said Dr. Mochon. “Obviously they are more comfortable, but they can also be a safer method for patients who have nasal conditions, such as chronic nose bleeds and nasal polyps. If you suffer from one of these conditions you should speak with your provider about what sample type will best meet your needs, but, when possible, nasopharyngeal samples should be the primary method of collection.”

Testing the sample in the laboratory

After the swab is collected, it is placed into a liquid, which is referred to as transport media, and sent to the laboratory to be processed and tested. In fact, you may be surprised to learn that the lab processes each of the swabs (nasal, NP and throat) exactly the same.

This is because the swabs used in the collection process are looking for the same thing — the virus in respiratory secretions and infected cells. Once the swab is placed into the transport media it is designed to release the virus and the infected cells into the liquid. Tests are then performed using this liquid.

Saliva

Dr. Mochon spoke enthusiastically about this sample type.

“Some early data from various laboratories across the country have shown that saliva may be as reliable as the NP swab.”

He went on to say that if saliva is shown to be a reliable and accurate sample type this will lead to a more comfortable experience for the patient and lessen the need for swabs as part of the collection. "This is very promising both for patients and medical professionals.”

Dr. Mochon explained that the deeper, NP swabs can sometimes induce sneezing or gagging, which can then aerosolize the virus.

Healthcare workers wear masks and other protective gear, so as to keep them safe when running NP swabs. This is not a problem with saliva as the patient would simply spit into a tube or a cup.

Pooling

In this method, samples from multiple patients are combined together and tested. If negative, then it is assumed that all are negative. If positive, then the laboratory will retest each patient individually.

The rationale behind this method is to increase the testing capacity of the laboratory and save on testing reagents, which have also been limited due to the size and scope of the COVID-19 pandemic. This method can only be used if the prevalence of the virus is below 5-6%.

Should I get tested?

These tests are becoming more widely available, but they are still reserved primarily for people showing symptoms.

If you are not showing symptoms, you might want to learn more about the antibody test.

If you are showing symptoms related to COVID-19, visit our symptom checker at bannerhealth.com for information on next steps.

Bobby Boland is a contributing writer for Banner Health.