Cortisol Analysis Using a Novel Method of Saliva Collection: Method and Application in Preterm Infants

Preterm infants experience frequent stressors that activate the hypothalamic-pituitary-adrenal (HPA) axis. Cortisol can be readily quantified in saliva samples, but sufficient saliva volumes are difficult to collect from preterm infants. We report the development and validation of a novel method to collect saliva using flocked polyester swabs and the application of this method in a study of preterm infants. Saliva samples, collected from adult participants (N = 24), were divided and processed as "standard" aliquots and aliquots absorbed by and extracted from flocked polyester swabs. Cortisol levels in "standard" and "swab" aliquots were compared. We then collected saliva samples from preterm infants (N = 31) using flocked polyester swabs to measure HPA responses to routine, clustered nursing care. Saliva samples were collected from each infant prior to caregiving, 30-min after caregiving, and 60-min after caregiving. Aliquots from the same adult were highly correlated. Sufficient volumes of saliva were extracted from 91 of 93 infant swabs (98%). Changes in cortisol levels from baseline to 30-min and 60-min after caregiving were negatively associated with acute procedural stress, quantified using the Neonatal Infant Stressor Scale. The change in cortisol level from baseline to 60-min after caregiving was negatively associated with caregiving duration. Further research is needed to understand the relationship between caregiving stress exposure and HPA axis responses in preterm infants and to identify the myriad factors that may influence this association. Flocked polyester swabs offer a viable option for the collection of sufficient volumes of saliva to support this research.