The relationship of salivary and cord blood cortisol in preterm infants.

Recent studies reveal that salivary cortisol measurements accurately reflect blood cortisol levels in older children and adults; yet, the relationship between the two values in premature infants has not been established. This study explores the use of salivary cortisol as an accurate measure of adrenal steroid concentrations in premature infants to provide a reliable and less invasive tool for investigating hormonal stress response. Premature infants (n=51) were recruited, with saliva and blood collected immediately after birth, and cortisol levels measured by radioimmunoassay. A linear relationship emerged between cord plasma and salivary cortisol values in the 102 paired samples [(salivary cortisol) = 0.546 +/- 0.192 x (plasma cortisol), r = 0.481 and p = 0.0003]. Findings demonstrated that salivary and plasma cortisol levels were correlated in premature infants. This information will be useful in future studies that assess use of salivary cortisol to evaluate neonatal stress axis function.