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Introduction

Laurie Carter, DDS, PhD

Past President, IADR Diagnostic Systems Group, Symposium Organizer

Saliva and other oral fluids support a host of functions in the oral cavity. These fluids reduce biomass and provide mechanical cleansing of teeth, provide an optimal pH in which oral functions are efficiently carried out, and contain an array of antimicrobial components. Saliva is not merely an ultrafiltrate of plasma; it contains the entire library of proteins, hormones, antibodies, and other molecular compounds which are typically measured in routine blood tests. Thus, saliva functions as a diagnostic window to the body, both in health and in disease.

Oral samples include saliva, as well as gingival crevicular fluid, buccal swabs, and mucosal transudates. Saliva, as a diagnostic medium, is easy to collect and poses none of the risks, fears, or invasiveness of drawing blood. Salivary diagnostic tests could eliminate the need not only for a trained technician but also of the potential risk of contracting infectious disease for both a technician and the patient.

In addition, salivary diagnostics offers point-of-care testing and real-time surveillance. The potential value of a portable diagnostic test which could provide results in real time in the clinician’s office or on site in the field is limitless. For instance, reduction in unnecessary antibiotic use would have a positive impact on the growing problem of antibiotic resistance. The principal utility of a diagnostic screening test resides in its ability to modify the pre-test likelihood of disease. Salivary diagnostic tests would also be popular and convenient for patients who need to monitor their own hormone or medication levels on an ongoing basis. Moreover, salivary diagnostics is ideal for use in community outreach and surveillance studies and in markets in which rapid results and inexpensive technologies are essential.

Scientists have long recognized saliva as a mirror of the state of the body’s health. Until recently, the problem with developing the field of salivary diagnostics was that specific and informative biomarkers exist in saliva in relatively low quantities. However, the development of new, exquisitely sensitive amplification techniques—such as RT-PCR, Q-PCR, and high-density oligonucleotide microarrays—has demonstrated the feasibility of using saliva as a diagnostic probe for the rapid and unambiguous detection of oral biomarkers.

Currently, a cadre of scientific groups is advancing the development of micro- and nanotechnology-based biosensors to detect salivary biomarkers. Current efforts also focus on cataloguing the human salivary proteome. Future efforts will determine differences in salivary biomarkers from healthy controls compared with those in patients with a variety of diseases and disorders. These ‘labs’ on a silicon chip will efficiently scan oral fluids for the presence or absence of biomarkers catalogued in a database to be linked to systemic diseases and conditions.

Use of saliva for the detection of those using illicit drugs has increased dramatically in the workplace setting. Saliva is collected directly under observation, which eliminates adulteration and substitution concerns involving urine samples, and offers a window into the individual’s status at the time of testing. It is envisioned that salivary diagnostic tests will be used as ‘canaries’ on a chip to detect environmental, occupational, and biological exposures—which, among other issues, has important implications for bioterrorism surveillance.

Testing for HIV positivity is one example of a powerful use of saliva in the diagnosis of infectious diseases. Early efforts indicate that there exist differences in patterns of mRNA expression in saliva that would indicate the presence of a developing oral squamous cell carcinoma. Salivary mRNA may serve as a chemical signature that a particular gene has been expressed. There is also evidence that saliva may be useful for monitoring the presence of biomarkers indicating the presence of neoplasia in remote sites—for instance, breast cancer. Salivary diagnostic tests may provide an avenue to allow for detection of malignancies at a sufficiently early stage that treatment is likely to be successful, and to provide inexpensive testing which will reduce affordability and accessibility barriers to early diagnosis.

The use of saliva as a diagnostic probe represents an enormous translational research success story. The papers presented in this symposium highlight the remarkable technological and molecular advances which are revolutionizing the discipline of saliva-/oral-fluid-based diagnostics.

We would like to thank OraSure Technologies, Procter & Gamble, and Comprehensive Nursing Care for their support as corporate sponsors of this symposium.

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