Predictors and patterns of participant adherence to a cortisol collection protocol

Cortisol, a stress-related hormone, has been measured in many psychoimmunological studies via collection of saliva; however, patterns of participant adherence to protocol procedures are rarely described in the literature.

In this paper we examine adherence to a cortisol morning rise collection protocol and explore its associations with demographic predictors and fatigue.

Participants included 262 breast cancer survivors enrolled in a National Institute of Nursing Research funded longitudinal intervention study (5R01NR010190, M. Mishel, P.I.). Self-reported times of salivary cortisol collection were recorded for each of 12 saliva samples. Adherence was assessed with respect to various demographic factors and fatigue. Participants were categorized as having high, moderate, or low adherence to the saliva collection protocol.

Overall, 117 (45%) participants had high adherence to the protocol, 117 (45%) participants had moderate adherence, and 28 (∼11%) participants had low adherence. Tests for proportionality for the polytomous logistic regression indicated that demographic predictors in our model had a similar association with each level of participant adherence. Women who did not adhere to the saliva collection were more likely to be African American (OR .50, CI .29-.88) and to report a high impact of fatigue on their behaviors (OR .88, CI .79-.98). Though other predictors in the model were not statistically significant (working full-time and living with at least one child under 18 years of age), the overall model was significant (χ(2)(4)=17.35, p<.01).

To our knowledge, this is the first study to examine profiles of participant adherence to a cortisol sampling protocol over multiple timepoints. By conceptualizing adherence as a polytomous outcome, future studies may give us insights into adherence trends in other populations with the aim of promoting adherence and designing more informed saliva collection protocols.