Background and aims: The increased use of salivary cortisol as a biomarker of stress and/or diurnal rhythms has facilitated research of Hypothalamic-pituitary-adrenocortical (HPA)function. Saliva collection remains problematic with preterm infants. The twofold purpose of this study is to 1) establish validity of the filter paper method for saliva collection and 2) apply the filter paper method for saliva collection to preterm infants.
Design and measures: Whole saliva was collected from six normal adult subjects to create a pool. Validation measures included comparison of levels obtained from whole saliva and filter paper, an evaluation of storage effects, assessing spiking recovery, and measurement of linearity of dilution. In the application study, saliva was collected every three hours, before feedings for three consecutive days from 26 hospitalized preterm infants. Diurnal variation in cortisol was examined using hierarchical linear modeling and individual calculation of diurnal pattern using an accepted technique.
Results: Validation studies revealed acceptable recovery of whole saliva from filters, no effect of room temperature storage of filters for up to six months, and acceptable linearity of dilution up to 4. Saliva from preterm infants was easily collected. Only 2% of the samples were lost due to inadequate wetting of the filters. An inverse association was found between postconceptional age and one-minute APGAR scores and infant cortisol levels. Variable daily cortisol patterns and no discernable rhythm were found for this sample; however, four infants appeared to show atypical diurnal pattern.
Conclusions: The filter paper method is a valid method of saliva collection that is feasible to use with preterm infants.