Saliva testing
Saliva is a useful biological fluid for assaying steroid hormones such as cortisol, genetic material like RNA, proteins such as enzymes and antibodies, and a variety of other substances, including natural metabolites, including saliva nitrite, a biomarker for nitric oxide status (see below for Cardiovascular Disease, Nitric Oxide: a salivary biomarker for cardio-protection).
Salivary testing has even been used by the U.S. government to assess circadian rhythm shifts in astronauts before flight and to evaluate hormonal profiles of soldiers undergoing military survival training.
Additionally, since multiple samples can be readily obtained, saliva testing is particularly useful for performing chronobiological assessments that span hours, days, or weeks.
Recent applications emphasize the development of increasingly sophisticated techniques to detect additional proteins, genetic material, and markers of nutritional status.
"[9] Most saliva testing is performed using enzyme-linked immunosorbent assay (ELISA), polymerase chain reaction (PCR), high-resolution mass spectrometry (HRMS), or any number of newer technologies such as fiber-optic-based detection.
This type of testing typically involves collection of a small amount of saliva into a sterile tube followed by processing at a remote laboratory.
Some methods of testing involve collecting saliva using an absorbent pad, applying a chemical solution, and monitoring for color change to indicate a positive or negative result.
[13] In situations where a subject undergoes induced anxiety, high cortisol levels correspond with experiencing more physiological symptoms of nervousness, such as increased heart rate, sweating, and skin conductance.
Alpha amylase levels in saliva provide a non-invasive way to examine sympathoadrenal medullary (SAM) activity, which can otherwise be measured with electrophysiological equipment or blood plasma readings.
Furthermore, by testing alpha amylase levels, scientists noticed a difference in reactivity behavior among individuals with previous experience in a similar situation.
[17] While saliva testing has the promise of becoming a valuable and more widely used tool in psychological research in the future, there are also some disadvantages to the method that must be kept in mind, including the cost of collecting and processing the samples and the reliability of the measure itself.
In 2008 the Endocrine Society published diagnostic guidelines for Cushing's syndrome, wherein they recommended midnight salivary cortisol testing on two consecutive days as one possible initial screening tool.
[26] A 2009 study examined the use of saliva testing to measure estradiol, progesterone, dehydroepiandrosterone (DHEA), and testosterone levels in 2,722 individuals (male and female).
"[34] A 2007 article reported that the free testosterone measurement, including via saliva assay, represents "the most sensitive biochemical marker supporting the diagnosis of PCOS.
Researchers determined that the accuracy of saliva testosterone and DHEA measurement exceeded 98.5% and that this method "has satisfactory applicability" in the diagnosis of late-onset hypogonadism.
Researchers found that sixty-five proteins, the majority of which are involved in regulating metabolism and immune response, were significantly altered in type-2 diabetics.
[54] The accuracy of saliva anti-HIV antibody testing has been confirmed by many additional studies, leading to approval of this method by the U.S. Food & Drug Administration in 2004.
[56] Other studies found that saliva assay for anti-HAV antibodies (IgM and IgG) was an effective method to identify HAV-infected individuals.
[60] In 2004 El Hamshary and Arafa found that salivary anti-E. histolytica IgA concentration had "predictive diagnostic value of intestinal amoebiasis…as well as in tissue amoebiasis.
[63] A study published in 1990 demonstrated the diagnostic utility of saliva IgG testing in identifying neurocysticercosis secondary to Taenia solium.
Based on their results, researchers concluded that saliva testing could serve as a reliable non-invasive detection method for H. pylori infection.
[67] A 2010 study found that elevation of three saliva biomarkers (MMP-8, TIMP-1, and ICTP), particularly when analyzed using time-resolved immunofluorometric assay, was suggestive of periodontitis.
[68] In 2011 Punyadeera, et al., studied "the clinical utility of salivary C-reactive protein levels in assessing coronary events such as myocardial infarction in a primary health care setting.
Sobko et al. shows that Japanese traditional diets rich in leafy vegetables elevated both plasma and saliva nitrite levels with a corresponding decrease in blood pressure.
Here, they showed ingestion of beet juice, a nitrate-rich food, by healthy volunteers markedly reduced blood pressure and by disrupting saliva, either by spitting or interrupting the bioconversion of dietary nitrate to nitrite in the mouth with anti-bacterial mouthwash, the chemical reduction of nitrate to nitrite to nitric oxide with an associated decease in blood pressure was abated.
[80][81][82] Monitoring the bioconversion of plant-derived nitrate into salivary nitrite serves as a surrogate biomarker for total body nitric oxide status.
Researchers found that several drug metabolites were detected more frequently in saliva than in urine; this was true for 6-monoacetylmorphine, amphetamine, methamphetamine, and N-desmethyldiazepam.
[9] Advances in ELISA and mass spectrometry, in addition to the emergence of novel detection methods that take advantage of nanotechnology and other technologies, are enabling scientists and practitioners to achieve high analyte sensitivity.
This issue is currently being addressed through identification of multiple biomarkers that are correlative of a disease; these can then be screened concomitantly to create a comprehensive panel of tests that significantly increases diagnostic specificity.
As the research community continues to validate and refine test methods and establish standard diagnostic ranges for various saliva biomarkers, this issue should be resolved.
