Table 2.

Steps to improve study design when measuring human oxytocin concentrations.

Issue	Concern	Proposed solution
Choosing the type of sample (CSF, plasma, saliva, urine) for oxytocin measurement.	The type of sample used reflects different information.	When possible, obtaining human CSF for measurement of oxytocin can provide information about central processes. However, since this is typically impractical, most studies involve peripheral measurement. In humans, the kinetics of production and clearance have only been established for plasma oxytocin concentrations [2]. Thus, until these can be defined for human oxytocin concentrations in serum, saliva, and urine, we recommend using plasma oxytocin measurement when possible.
Deciding to examine baseline levels or changes.	Variability in oxytocin secretion/levels.	Assessments of baseline levels require numerous assessments [34]; assessments of pre-post changes should include at least 2 time points to measure reactivity, and at least 3 time points to measure recovery.
Inconsistency in experimental paradigms used.	Do not know if findings are generalizable or task-specific.	Use reliable paradigms and perform direct replications.
Consideration of covariates.	Decreases precision and generalizability.	Include relevant covariates and refer to best practices for menstrual cycle variation for female participants [138].
Genetic/epigenetic studies often do not measure endogenous oxytocin concentrations.	Unable to test hypotheses about the relationship between oxytocin receptor genetic and epigenetic functional variation and endogenous oxytocin concentrations	Examine the relationship between oxytocin receptor genetic and epigenetic variants with functional significance and levels of endogenous oxytocin concentrations.
Underrepresentation of healthy males in studies measuring human endogenous oxytocin concentrations.	Results are not generalizable to males.	Include male subjects when appropriate.
Most human studies measuring endogenous oxytocin concentrations do not measure endogenous vasopressin concentrations as well.	There is a high degree of structural similarity and known cross-reactivity between oxytocin and vasopressin [1].	Measure endogenous concentrations of vasopressin in addition to oxytocin to bolster the validity of the oxytocin assay and to demonstrate specificity of oxytocin reactivity over vasopressin or vice versa [148]. Although this requires obtaining a greater sample volume, measuring endogenous vasopressin concentrations can serve as a methodological and experimental negative control.