Salivary and serum cortisol levels in newborn infants

Given that serum cortisol level interpretation in newborn infants (NBIs) is hard, the objective of this study was to correlate baseline salivary and serum cortisol levels and to describe salivary cortisol levels in the first month of life.

Descriptive, prospective, longitudinal, and correlational study. Term NBIs were selected from the Division of Neonatology of Hospital Nacional Profesor Alejandro Posadas in 2014. Cortisol was measured in saliva specimens while cortisol, cortisol-binding globulin, and albumin were measured in blood specimens. A linear correlation was performed to relate serum and salivary cortisol levels; Friedman test was conducted to compare cortisol levels during the first month of life, and the difference was used to analyze the performance of values equal to or lower than the first quartile.

Fifty-five NBIs were studied. Serum cortisol: 7.65 (1.0-18.1 gg/dL); salivary cortisol: 35.88 (5.52-107.64 mmol/L); cortisol-binding globulin: 22.07 (16.5-33.0 gg/mL), expressed as median and range. The correlation coefficient between serum and salivary cortisol was 0.54, P = 0.001. Cortisol performance during the first month of life showed no statistically significant differences, and the difference between the second and the first specimen of values equal to or lower than the first quartile increased in 10 out of 12 patients.

The measurement of cortisol in saliva reflects serum cortisol levels in normal NBIs. Some patients had low levels of cortisol at 36 hours of life and showed a trend towards a spontaneous increase during the first month of life.