|STUDENT FORUM COMMENTARY
|Year : 2015 | Volume
| Issue : 4 | Page : 156-158
Saliva: A fluid in search of a diagnostic use
School of Dental Medicine, University of Connecticut, Farmington, Connecticut, USA
|Date of Web Publication||27-Nov-2015|
School of Dental Medicine, University of Connecticut, Farmington, Connecticut
Source of Support: None, Conflict of Interest: None
Since saliva has been studied for more than 50 years and is relatively easy to collect, it is reasonable to ask why saliva is not in wider use as a diagnostic fluid. Here we discuss the criteria for diagnostic tests for diseases, barriers to use saliva for diagnostic testing, and the possibility of overcoming barriers to acceptance of saliva for diagnosis.
Keywords: Biomarker, diagnostic test, saliva
|How to cite this article:|
Liu J. Saliva: A fluid in search of a diagnostic use. Dent Hypotheses 2015;6:156-8
| Introduction|| |
Enter the words "saliva tests" in a browser search box and many entries are listed. The multiple pages of listings suggest that saliva tests are widely used. Unfortunately, this is not the case and blood and urine remain the body fluids of choice in medical tests. Since saliva has been studied for more than 50 years and is relatively easy to collect, it is reasonable to ask as to why saliva is not in wider use as a diagnostic fluid.
| Criteria For a Diagnostic Test For a Disease|| |
Whole saliva is an easily collected complex aqueous mixture containing inorganic components such as electrolytes, small molecular weight organic compounds such as urea, ammonia, uric acid, glucose, cholesterol, fatty acids, glycerides, lipids, glycolipids, amino acids, hormones, and large molecular weight compounds such as proteins and messenger RNA (mRNA). All components derive from the secretions of the major and minor salivary glands, oral mucosa transudate, mucous from the nasal cavity and pharynx, epithelial cells, serum, crevicular fluid, bacteria, and food debris. The predominant proteins in the saliva include enzymes, mucins, cystatins, and antibacterial proteins. More than 3,000 distinct proteins were detected in salivary proteome. ,
Salivary flow and composition are influenced by age, gender, individual hydration, body posture, lighting, smoking, circadian rhythms, and medications. For example, salivary Na, K, total protein, immunoglobin A (IgA), and amylase activity have been shown to increase linearly with age. Salivary composition has been observed to be influenced by systemic changes allowing the identification of biomarkers for disease conditions. The use of saliva as an alternative diagnostic tool to blood offers certain advantages due to its noninvasive and relatively stress-free collection methods. The practicalities of salivary analysis have been studied in many diseases such as viral and bacterial infections, autoimmune diseases, endocrinology, oncology, stress assessment, medication detection, toxicology, and forensics. Interestingly, recent studies also demonstrate the diagnostic utility of saliva with implications for cardiovascular disease, systemic and local inflammation, hepatic damage, and insulin resistance. ,
Despite its potential, only a few saliva tests have been established as a diagnostic tool. Currently, salivary diagnostic tests are available for various hormones, human immunodeficiency virus (HIV), and alcohol. Each test requires a small amount of saliva and produces rapid and accurate results. OraQuick, the Food and Drug Administration (FDA) approved in-home self-testing HIV kit, uses an oral sample for rapid detection of antibodies against HIV. Another FDA-approved enzyme immunoassay kit can be used for the measurement of salivary cortisol. This kit may be used to measure adrenal cortical function and as a screen for Cushing's and Addison's disease. 
| Barriers in the Use of Saliva For Diagnostic Testing|| |
There are numerous barriers to shift to the use of saliva as a diagnostic fluid away from blood and urine. In the United States, one barrier is the extensive network of laboratories available to test blood and urine. This network represents a significant financial investment in equipment and personnel, both phlebotomists and lab technicians, by industries devoted to testing. Another barrier is that blood tests have been used for hundreds of years with the results of a significant amount of baseline data for markers for reference and for specific diseases. As a result of this history, health care providers, physicians, dentists, physician assistants, nurses, and many others worldwide are familiar with blood test values. Therefore, the medical and research communities must first become aware of the potential of salivary diagnostics. 
In addition, although simpler to collect, saliva is more variable than blood and urine. Its composition is affected by the proportions of secretions from the different glands as well as a mixture of food debris, bacteria, and shed cells. For stimulated saliva collection, it is subject to inconsistent gustatory stimulation throughout the collection procedure. Finally, although antibody-based diagnosis seems promising, the small market for commercial antibodies specific to salivary analytes makes it very difficult to obtain kits and antibodies that have undergone a rigorous quality control.
| Overcoming Barriers in the Acceptance of Saliva For Diagnosis|| |
In what situations might saliva be better than blood as a test fluid? If a test is developed for home use, the fluid would have to be easily accessible.
An example of a home test displacing a blood test is the development of the home pregnancy test. The home pregnancy test was an immediate success not only because it used urine, a readily available body fluid but because the results were immediate. There was no need to "mail" samples to a laboratory and wait for days for the results. The success of the home pregnancy test tells us that for saliva to displace blood as a test fluid, a home test is needed and the test must provide information on something of interest and importance and the results must be immediate.
What kind of home-testing might people want to use? Several possibilities come to mind. For example, senior citizens may want something to test for Alzheimer's (salivary amyloid beta and tau proteins) in the privacy of their home, or millennials, concerned with life-work balance, might want a home test to monitor stress levels (saliva cortisol). Also, while at the gym, a test to monitor exercise efficiency (salivary lactic acid) might be useful. All these tests would use a sample of saliva and the presence of a certain level of biomarker presented and monitored using a smartphone. The results could be immediate. How this can be accomplished is of course waiting for the next Steve Jobs to be figured out.
But there are other uses of saliva tests that depend on the ease of sampling. For example, when a population needs to be screened, say for Ebola virus, or following a terrorist attack (Sarin gas in Tokyo subway), it is necessary to identify the toxic agent in order to administer an antidote. In such situations, drawing blood is not possible and a saliva test would be a good choice.
| The Future Belongs to Saliva|| |
Given the advances in the technology of testing, it is reasonable to consider that in the future more home-testing for disease diagnosis will occur. In this case, saliva is the ideal body fluid to be used in analysis. Saliva will not displace blood or urine for the monitoring of many diseases but the use of saliva will open an entirely new market for testing. Clearly, saliva must wait for technology to catch up with its utility. The future looks bright for saliva-testing.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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