Consisting of 99 percent water, saliva is a complex biofluid critical to many bodily functions, including facilitating taste and kicking off the digestion process. Do you have a favorite food? You can thank your saliva for that, as salivary proteins influence how food tastes to different people. Saliva also protects our teeth from decay and serves as a first line of defense against viruses, bacteria, and fungi. Beyond these basic functions, saliva is a versatile, yet underappreciated, diagnostic sample type.
A brief history from HIV to 23andMe
Researchers in the fields of epidemiology, psychology, sociology, and anthropology have long studied saliva. In the 1980s, researchers found that hormones like cortisol can be measured in saliva at concentrations similar to those in patients’ blood. This research helped popularized saliva testing as a minimally invasive, quick, and inexpensive alternative to blood and urine.
Over the past several decades, scientists have also recognized saliva as a potential sample type to screen for human immunodeficiency virus (HIV) infection, as it’s both easier and safer for medical professionals to handle and transport. Studies show that using saliva for the detection of HIV antibodies is as sensitive and accurate as testing blood—a promising development for the future of salivary diagnostics.
In 2017, saliva testing gained momentum with the U.S. Food and Drug Administration approving 23andMe’s Personal Genome Service Genetic Health Risk (GHR) tests. This test examines saliva samples for more than 500,000 genetic variants associated with increased risks of developing conditions such as Parkinson’s, late-onset Alzheimer’s, and Celiac disease.
Advantages of comfortable, cost-effective testing
The noninvasive nature of saliva collection is appealing to health providers and patients alike. Testing saliva, instead of blood, limits a health care worker’s potential exposure to blood-borne pathogens, including HIV, hepatitis virus, bacteria, and parasites. With blood draws, patients are at an equal risk of infection if the blood collection site is not properly sterilized. The simple procedure of saliva collection eliminates such risks and can be performed easily by patients in the presence of a provider. Furthermore, patients who have a fear of needles or are prone to fainting, bruising, and pain after blood collection may not think twice about providing a saliva sample.
Beyond being a safer and easier alternative to traditional biofluid (blood and urine) screenings, saliva testing is scalable in a way that other sample types are not. It can be used for the rapid testing of large populations to boost infectious disease testing and surveillance.
Because saliva testing is more economical than nasopharyngeal testing, it can be especially helpful in rural regions that have limited access to health care. In a study that examined the costs associated with SARS-CoV-2 testing, researchers found that collecting saliva samples can save about $636,105 for every 100,000 patients.
What’s next for salivary diagnostics
Research on saliva as a sample type for SARS-CoV-2 testing continues to grow in popularity, serving as evidence of the benefits associated with salivary diagnostics, including its low cost and scalability. Looking ahead, the market for salivary diagnostics can only be expected to grow as new biomarkers are discovered and validated.
As potential analytes are present in saliva at much lower concentrations than in blood, highly sensitive diagnostic technology is needed for saliva testing. Thus, standardizing the stages of saliva collection, handling, and storage is critical to ensure accurate and reproducible results.
To get the most out of saliva samples and overcome these challenges, clinical labs need to standardize their testing programs and invest in high-throughput workflows. If the industry can meet these challenges head-on, saliva collection may prove to be a major advance in diagnostics.