About COVID-19 PCR saliva testing

The quality of the COVID-19 saliva PCR test

The test is developed, validated, and performed in the UAB Diagnolita’s laboratory in compliance with the highest quality standards.  The state accreditation service has granted a license to provide the COVID-19 testing service.

The test sensitivity is over 99.98%, with a specificity of 100%. The biomedical study in cooperation with LSMU Kaunas Clinics and Kaunas Clinical hospital proved the efficacy of the test. The saliva PCR test demonstrated 98.15% Positive Agreement and 98.11% Negative Agreement with nasopharyngeal PCR tests used in clinical practice.

The Limit of Detection (LOD) of the test is 400 copies/ml of sample, and belongs to high-sensitivity tests. [The LOD of high sensitivity tests range from 100 to 1000 copies/ml (Savela ES et al., 2021)]. The test also complies the requirements of the V-2797 legislation, according to which the LOD must not exceed 1000 viral genome equivalents/ml of sample. 

Each sample is tested for SARS CoV-2 spike (S) and RNA polymerase (RdRP) genes and human endogenous RNase P RNA, which indicates the proper collection, transportation, and purification of the sample.

UAB Diagnolita employees follow information about the strains of the SARS-CoV-2 virus spreading in Lithuania and other countries and, if necessary, can quickly adjust the test. In this way, we ensure that the test remains reliable and accurately detects all known strains of the virus circulating in Lithuania.

How is the Diagnolita’s saliva COVID-19 PCR test performed?

Diagnolita’s COVID-19 PCR test uses a patient’s saliva sample. A test tube with a funnel ensures convenient saliva collection. The saliva stabilization medium added to the collected saliva dissolves the virus envelope, inactivates it and stops the virus from spreading and multiplying. The unique composition of the medium also stabilizes viral RNA. The stabilized sample is stored, shipped to the laboratory at ambient temperature, and registered. The nucleic acid is purified from saliva and tested for the presence of viral RNA by PCR. The test result is delivered to the electronic system E.sveikata, and the patient is informed by e-mail. A certificate confirming the result is issued on request for an additional fee.

Scientific information. A brief review of scientific publications on saliva PCR tests

The saliva PCR test is as accurate as the nasopharyngeal PCR test. 

Other authors have also shown that the sensitivity and specificity of saliva PCR tests are very similar to those of nasopharyngeal swabs, and the differences obtained are not statistically reliable (Nasiri K, Dimitrova A, 2021; Butler-Laporte G et al., 2021). Based on these results, saliva PCR testing is preferable because close contact with medical personnel is avoided during sample collection, thus reducing the risk of viral transmission (Nasiri K, Dimitrova A, 2021; Beyene GT et al., 2021). Another advantage of the salivary PCR test is that this method of testing is more suitable for testing children and individuals in quarantine (Butler-Laporte G et al., 2021).

Saliva PCR test detects viral RNA in asymptomatic and pre-symptomatic infected people.

A study published in Nature Medicine confirmed that the SARS-CoV-2 virus is detected in the cells of the oral epithelium and salivary glands of asymptomatic or pre-symptomatic infected people. Though the subjects did not experience symptoms of COVID-19, the virus in their saliva was infectious (Huang N et al., 2021). Another study published in Scientific Reports supports the suitability of the saliva test for testing asymptomatic people. During this study, saliva, nasopharyngeal and nasopharynx swabs were compared. The sensitivity of saliva PCR was similar to or better than that of nasopharyngeal and nasopharynx swabs (Teo AKJ et al., 2021).

Saliva PCR testing is beneficial for children

Parents often disagree testing their children using a nasopharyngeal swab because the sampling procedure is invasive and unpleasant. Therefore, in Zurich, Switzerland, saliva samples, which are easier to collect and non-invasive, have been considered an alternative to testing children. Examination of 170 children proved that the results of the saliva PCR test were in good agreement with those of the nasopharyngeal PCR test: percent positive agreement was 93.3%, and the percent negative agreement was 96.4%. Based on these results, mass PCR saliva testing for SARS-CoV-2 RNA from saliva samples started in schools in Zurich (Huber M et al., 2021).

REFERENCES:

1. Butler-Laporte G et al. Comparison of Saliva and Nasopharyngeal Swab Nucleic Acid Amplification Testing for Detection of SARS-CoV-2: A Systematic Review and Meta-analysis. JAMA Intern Med. 2021 Mar 1;181(3):353-360. doi: 10.1001/jamainternmed.2020.8876. Erratum in: doi: 10.1001/jamainternmed.2021.0245. PMID: 33449069; PMCID: PMC7811189.
2. Huang N et al. SARS-CoV-2 infection of the oral cavity and saliva. Nature medicine 2021. Nat Med. 2021 Mar 25.;doi: 10.1038/s41591-021-01296-8.
3. Huber M et al. High Efficacy of Saliva in Detecting SARS-CoV-2 by RT-PCR in Adults and Children. Microorganisms 2021, 9(3), 642. https://doi.org/10.3390/microorganisms9030642.
4. Teo AKJ et al. Saliva is more sensitive than nasopharyngeal or nasal swabs for diagnosis of asymptomatic and mild COVID-19 infection. Sci Rep. 2021 Feb 4;11(1):3134. doi: 10.1038/s41598-021-82787-z. PMID: 33542443; PMCID: PMC7862309.
5. Nasiri K, Dimitrova A. Comparing saliva and nasopharyngeal swab specimens in the detection of COVID-19: A systematic review and meta-analysis. J Dent Sci. 2021 Jan 29. doi: 10.1016/j.jds.2021.01.010. Epub ahead of print. PMID: 33558826; PMCID: PMC7846225.
6. Beyene GT et al. Saliva is superior over nasopharyngeal swab for detecting SARS-CoV2 in COVID-19 patients. Sci Rep. 2021; 11: 22640. doi: 10.1038/s41598-021-02097-2. PMID: 34811429; PMCID: PMC8608806.