New COVID-19 Saliva Test Showed Very High Sensitivity and Specificity Rates: Study
Tue, April 20, 2021

New COVID-19 Saliva Test Showed Very High Sensitivity and Specificity Rates: Study



A new COVID-19 test has been developed in a fertility center. It is designed to detect the presence of the SARS-CoV-2 virus in saliva samples. If it becomes available on a wide scale, it may speed up results turnaround and support mass testing.

The innovative COVID-19 saliva test was developed by scientists at Columbia University, a private research university in the US. Unlike the standard PCR test utilized to detect the virus in nasal swab samples, the new test simply relies on saliva samples and does not require expensive instruments and proprietary components. Although not yet commercially available, it has been tested and found with a very high accuracy rate – similar to a PCR system. They published their findings in the journal medRxiv.


A New COVID-19 Test That May Push Mass Testing

Currently, the most reliable, commercially available test for COVID-19 is the polymerase chain reaction or PCR test. The test requires nasal swab samples from a person and detects the presence of the virus, regardless if that person developed antibodies. It means that the PCR test has the highest accuracy in determining who may be infected with COVID-19 because it recognizes the pathogen, not antibodies, as opposed to the rapid antibody test.

Unfortunately, a PCR test requires expensive equipment and specific components, depending on the configuration and manufacturer. A PCR system happens to require these things due to compatibility issues. As such, some governments have to purchase more expensive parts to work with their existing testing capabilities. Otherwise, existing machines cannot be optimized to test COVID-19.

Aside from being expensive and in-demand, PCR tests are unreliable when it comes to completion time. With the pandemic still bombarding communities, people want a test that can provide rapid and reliable results. But the PCR test for COVID-19 can take at least 24 hours to give an accurate reading. In some cases, the turnaround time can be up to a few days. This is a significant adverse force in quarantine facilities. The longer it takes for results to come out, the longer suspected individuals have to stay in those facilities. The same applies to suspected patients who have been admitted to hospitals.



At Columbia University, scientists created a new test for the novel disease: a test requiring saliva samples. It was an adaptation of a technology utilized for detecting genetic abnormalities in embryos prior to implantation. As the purpose suggested, it was developed in a fertility center to provide fast, reliable results for fertility treatment.

"We realized that the same technology that we use to help create lives could be repurposed to help save lives during the COVID-19 pandemic. The test serves a critical need for more widespread testing to help us safely reopen economies closed by the pandemic and prevent future outbreaks," said Dr. Zev Williams, a corresponding author of the study and chief of the division of reproductive endocrinology at Columbia University Irving Medical Center.

The most substantial aspect of the PCR testing process is the extraction of viral RNA from the sample. It is possible if a testing center is equipped with specialized instruments, which are expensive. But not every facility can do the entire testing process, and so, they have to rely on those equipped with instruments. Thus, the shipping of samples is a typical occurrence for extracting the RNA.

Unlike PCR tests, the novel saliva-based test removes the extraction aspect to speed up the process. The new test needs a saliva sample placed into a tube, which contains particular enzymes and reagents to identify the viral RNA. The same tube is placed next into a heat block or water bath to keep the sample warm throughout the reaction time. After 30 minutes, the sample inside the tube turns yellow to confirm the viral RNA. If the sample lacks the RNA of SARS-CoV-2, it will turn red. This method in detecting viral RNA, however, is not new in medical science.




Sensitivity and Specificity Rates

The true basis of the saliva test is the DNA amplification technique called loop-mediated isothermal amplification or LAMP. Compared to PCR tests, LAMP tests use a single temperature via a heat block or water bath. At the same time, the simplicity of LAMP tests allows authorized personnel to see the results with an unaided eye. That is possible with colorimetry or the science of describing and quantifying outcomes using the human color perception.

Scientists were able to repurpose the test for COVID-19 after exchanging specific substances. Normally, LAMP tests would have lower sensitivity due to compounds present in saliva and the usual reagents. For that, they utilized alternate buffers and enzymes to enhance the sensitivity rate. When compared to a standard LAMP test, their version exhibited more than 1000 times sensitivity in saliva samples.

For the specificity rate, the team obtained 60 samples and used them to assess the performance of their test. Out of 60 samples, 30 have SARS-CoV-2 and 30 lacked the virus. They also included 18 other samples collected from patients. The 18 samples were tested before with RNA extraction and RT-PCR test. Results showed that the new test correctly identified all samples, which tested negative in the Roche 6800 PCR system. That gave a 100% specificity rate. In 30 positive samples, the new test correctly identified 29 positive samples that reflected a specificity rate of 97%. And lastly, the test had no cross-reactivity with 19 other bacteria and viruses, including other coronaviruses, associated with respiratory illnesses.

According to the July 9, 2020 report by the World Health Organization of the United Nations, the total laboratory-confirmed cases of COVID-19 were 11,875,226 worldwide. More than 50% of those or 6,125,802 cases were confirmed in the Regions of the Americas. While the total deaths linked to laboratory-confirmed cases were 545,481 globally. Almost 50% of those or 272,606 cases were reported in the Americas as well. Unfortunately, the nations in the region are unable to conduct mass testing to completely map the presence of COVID-19.

The scientists are now working to obtain regulatory approval from concerning entities. They wanted to gain approval to implement the new test in patients. If approved, it will help evaluate the performance of the method in real-world settings. If it succeeds, it may help push mass testing.