Integration of salivary biomarkers into developmental and behaviorally-oriented research: Problems and solutions for collecting specimens
Introduction
Saliva has been championed as a diagnostic fluid of the future [1]. Much of the attention saliva receives as a biological specimen is due to the perception that the nature of sample collection is quick, uncomplicated, and non-invasive [2]. The literature suggests that in most cases this perception matches reality. Yet, in specific circumstances and populations, collecting saliva can be unexpectedly difficult, time consuming, and may require considerable creativity (e.g., [3], [4], [5]) to gather sufficient sample volumes for assay. When sample collection is inadequate and assay protocols or laboratory technicians cannot accommodate a partial sample, the missing data problems created can seriously compromise research, and hinder screening and potential diagnostic agendas.
In this report, we review the nature of some of the unique problems specific to the application of salivary biomarkers in developmental science and rigorously evaluate approaches to saliva collection that have been used in an attempt to resolve some of the difficulties with more traditional approaches. We present alternatives that can be used by investigators, especially in special circumstances and with unique populations of research participants, to improve the next generation of studies. We expect our findings will ease the burden on research participants and research assistants, reduce the rates of missing values in salivary data, and consequentially increase the probability of the successful integration of salivary biomarkers into behaviorally-oriented research.
Section snippets
Saliva collection: unexpected challenges
Contrary to popular belief, under certain circumstances, the collection of saliva can be cumbersome, time consuming, and frustrating for research participants and assistants. This appears to be true for the very youngest and also the very oldest age group of research participants.
Consequences when saliva collection is problematic
A variety of potentially negative consequences occur when saliva collection is ineffective. The most obvious is that missing values are created in data sets. Given that this phenomenon is potentially associated with ethnicity, poverty, medication use, age, and perhaps patience and persistence of individual research assistants, “missingness” is unlikely to be random. Non-random missing data significantly complicates multivariate statistical models of individual differences. For instance, this
All saliva collection devices do not perform the same: A closer look
The most common strategy for saliva collection in studies of adults involves the use of a cotton pledget (10 × 37 mm) to absorb sample from the participant's mouth. Commercially available saliva collection devices often employ cotton absorbent materials (e.g., Salivette, Sarstedt). Briefly, after 2–3 min in the oral cavity the cotton becomes saturated (appearing matted or flattened) with saliva. It is then removed from the subject's mouth, and saliva is expressed out of the cotton into a
Solutions to problems with saliva collection
In an attempt to solve the problems that cotton absorbent materials create for saliva collection in studies of early childhood, several possibilities have been explored. In this section, we first review attempts to stimulate saliva flow to increase the volume of sample available to be absorbed as well as the reduction of sample test volume requirements in immunoassays. Then we evaluate alternative sample collection strategies and characterize their relative advantages and disadvantages.
General conclusion
Taken together, our observations underscore that the collection of saliva in the very young and the oldest-old research participants can be unexpectedly challenging. Traditional saliva sampling techniques that involve the use of cotton materials to absorb sample have limitations that restrict their utility in these special circumstances and unique populations. The nature of this problem involves the very small amounts of saliva available to be collected, and the poor recovery of small volumes
Acknowledgements
This research was supported in part by the Behavioral Endocrinology Laboratory and the Child Youth and Families Consortium at The Pennsylvania State University as well as the Family Life Project funded by the National Institute of Child Health and Development (PO1HD39667-01A1). Thanks are due to the Family Life Project Investigators; student assistants, Claire Kang, Kathryn Sawruk, Jeff Marguin, Olga Rumyanstseva, Rachel Anolik, Reneca Green, Lauren Davis and Erin Kelly; and Mary Curran for
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