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Use of salivary cortisol measurements in young infants: a note of caution
C L Magnano1, E J Diamond, J M Gardner
1City University of New York.
Insights
Infant formula and breast milk can contaminate infant saliva cortisol tests. Defatting and extraction are crucial to remove interfering substances and ensure accurate salivary cortisol measurements in newborns.
Area of Science:
- Biochemistry
- Pediatric Endocrinology
Background:
- Salivary cortisol measurements are vital for assessing stress and adrenal function in infants.
- Infant formulas and breast milk are common sources of dietary intake for young infants.
- Potential for contamination of biological samples with milk products exists.
Purpose of the Study:
- To investigate the potential contamination of infant saliva samples with formula or breast milk during cortisol assays.
- To determine the accuracy of salivary cortisol measurements in young infants when milk products are present.
Main Methods:
- Cortisol concentrations were measured in 3 common infant milk formulas and breast milk.
- Samples were analyzed before and after defatting and extraction using a radioimmunoassay kit.
- Salivary cortisol levels in newborn infants were used as a reference.
Main Results:
- Cortisol concentrations in milk samples before defatting/extraction were significantly higher (1.64-82.80 µg/dL) than reported infant salivary levels (0.09-2.08 µg/dL).
- Post-defatting and extraction, milk cortisol concentrations decreased substantially (0.02-0.15 µg/dL), indicating interference from non-cortisol substances.
- High levels of cortisol and interfering substances in milk can falsely elevate infant salivary cortisol readings.
Conclusions:
- Formula and breast milk contain substances that can interfere with salivary cortisol assays in infants.
- Routine defatting and extraction of saliva samples are recommended for young infants to ensure accurate cortisol measurements.
- Implementing appropriate controls is essential for reliable salivary cortisol testing in pediatric populations.
Abstract:
In order to investigate possible contamination of saliva samples with formula or breast milk obtained from young infants for cortisol assays, we measured cortisol concentrations in 3 common infant milk formulas and in breast milk before and after defatting and extraction using a commercial radioimmunoassay kit. Cortisol concentrations obtained prior to defatting and extraction were equal to or higher than (1.64-82.80 micrograms/dL) levels reported for salivary cortisol levels reported in newborn infants (0.09-2.08 micrograms/dL). Cortisol concentrations obtained after the defatting and extraction were lower (0.02-0.15 micrograms/dL), indicating that values obtained prior to defatting and extraction were due to cross-reacting substances as well as cortisol. As saliva samples are not routinely defatted or extracted prior to being assayed, high cortisol levels and interfering substances in formula and breast milk could contaminate salivary cortisol measurements in young infants. The present study suggests that appropriate controls should be taken when making salivary cortisol measurements in young infants to help ensure accurate results.