Quixplained graphics: What are saliva tests, and how do they work?

Saliva tests for Covid-19: how does it work? Has it been tested? How is it different from RT-PCR tests? What are its advantages, and limitations? All your questions answered.

• By: Explained Desk
• New Delhi | Updated: August 27, 2020 09:26 AM IST
2 min read

How do the two tests compare?

On August 15, the US Food and Drug Administration (FDA) approved a new method of testing for Covid-19 — processing saliva samples — and termed it “ground-breaking”. It issued emergency-use authorisation to Yale School of Public Health’s diagnostic kit, called SalivaDirect. “This is the fifth test that the USFDA has authorised that uses saliva as a sample for testing,” it said.

Like RT-PCR, a saliva test too detects the virus. It converts the virus RNA into DNA, then amplifies the DNA to detect presence of the virus.

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What makes the SalivaDirect kit unique is that the Yale researchers have done away with a separate step or specialised equipment to extract the virus RNA.

“Our approach can be broadly implemented as it does not require saliva collection tubes containing preservatives and does not require specialized reagents or equipment for nucleic acid extraction,” the Yale study states.

So, how does it work? Has it been tested? How is it different from RT-PCR tests? What are its advantages, and limitations? All your questions answered:

The saliva test was first tested on a group of NBA players and support staff. The saliva test is less invasive that the RT PCR test. saliva “does not require a certified swab and collection receptacle and does not necessarily have to be obtained by a skilled healthcare provider, both of which increase diagnostic-associated costs”. A saliva test is reported to be prone to less error than has been reported in nasal swab collection, which sometimes give false negatives.

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