Saliva vs swab test – what’s the difference?

This week, we were excited to launch our COVID-19 Saliva PCR test. As a not-for-profit on a mission to provide accessible and affordable testing to all, we are proud to offer the test at an affordable price.

Since the outbreak of COVID-19, diagnostic testing has been an essential element in controlling the ongoing pandemic.

The vast majority of testing has been carried out using PCR nasopharyngeal (swab) tests. The NHS are currently using swab tests for patients and staff, as well as the wider public. However, we have since seen new sampling methods emerge, including saliva tests.

But what is the difference between a swab and saliva test? Are there any benefits of a saliva test?

Firstly, let’s look at what a PCR Test is:

PCR is a widely used laboratory method that stands for Polymerase Chain Reaction. The test detects the genetic material in the virus called RNA. When the sample reaches the lab, a solution known as ‘reagent’ is added to it. If there is a virus present the reagent starts a ‘chain reaction’ and creates billions of copies of the genetic material in the virus so that there is enough that it can be detected and analysed by scientists to provide a positive result.

A PCR swab test uses a swab to take a sample from the nose and throat. The swab is then usually sent in a test tube to a lab to be analysed for the virus.

A PCR saliva test uses a small saliva sample that is usually collected in a tube that has a mixing agent in, similar to the swab test, it is then sent away to be analysed.

Benefits of Saliva PCR Testing

Potential minimisation in exposure

The use of self-collected saliva has the potential to minimise the exposure to the virus protecting others, especially health care workers who are more likely to be exposed.

Swab tests can cause patients to cough and sneeze when being administered, increasing the chance of healthcare workers being exposed to virus particles putting them at risk.

Less invasive

Swab tests involve taking a sample from the back of the nose and throat of a patient.
This can be an uncomfortable and traumatic experience, especially for children and elderly patients. Some patients have even reported discomfort from swab tests including nosebleeds, nasal discomfort, headache, earache and rhinorrhea which can last hours to a day.

One of the biggest concerns of this is that patients might be reluctant to receive further testing if they previously experienced an uncomfortable test. Unlike swab tests, saliva testing is non-invasive.

Widespread shortages of swabs and personal protective equipment (PPE)

PPE is an essential part of protecting healthcare workers and individuals working in industries that put them at risk of exposure. But since the start of the pandemic, the demand for PPE has been higher than ever before, which has led to shortages around the world.

To provide an example, since the start of the pandemic, more than 5.6 billion items of PPE have been delivered to the health and social care system in England alone.

But what do saliva tests have to do with this? Because the self-collection of swab testing is more complicated for an individual to administer themselves, results can be less reliable which can be unfavourable for home testing. Saliva tests are easier to use so can provide higher reliability making it a better option for home testing, reducing the demand in PPE.

Just like PPE, there has been a demand in swab testing. Shortages in tests have even led to NHS staff absences due to staff having to self isolate as they were unable to receive a test. There have also been many reports of people unable to require a test or having to travel over an hour to their nearest testing facility. Saliva testing can help fulfil this demand, providing more tests for when people need them.

Which is more accurate? Swab or saliva?

The saliva test is highly accurate at detecting both symptomatic and asymptomatic individuals.

The viral load of SARS-CoV-2 in saliva has been studied across 355 samples from staff and patients at Yale-New Haven by the Yale IMPACT research team and Yale University School of Medicine. The team classified saliva samples into low (saliva viral load=3.212-4.4031 Log10 [Log](GE/ml)), medium (saliva viral load=4.4031-6.1106 Log (GE/ml)), and high (saliva viral load=6.1106-10.320 Log (GE/ml)) brackets.

The Nonacus PCR technology was validated together with the Department of Health and Social Care and found to have a limit of detection of 2.39 Log10 or 250 copies/mL which is capable of detecting viral load categorised as low in the Yale research with considerable margin.

The Nonacus manufactured reagents are CE-IVD marked for both saliva and swab sample types, and were found to have sensitivity of 98.35% and specificity of 99.3% using samples spiked with patient viral material provided by Department of Health and Social Care in validation work carried out in December 2020.

Further research has found that “saliva is a viable and more sensitive alternative to nasopharyngeal swabs and could enable at-home self-administered sample collection or accurate long-scale SCARS-CoV-2 testing.”

This isn’t to say that swab testing is an in-effective and inaccurate method of testing. However, with the shortages in PPE and swabs, risk to health workers and invasive sampling, saliva looks to be a strong competitor.

Find out more about our Saliva PCR Test here.