Hair cortisol as a potential biologic marker of chronic stress in hospitalized neonates

Background: As preterm and term infants in the neonatal intensive care unit (NICU) undergo multiple stressful/painful procedures, research is required that addresses chronic stress. Objectives: To determine whether (a) hair cortisol levels differed between term and preterm infants exposed to stress in the NICU and (b) an association exists between hair cortisol levels and severity of illness or indicators of acute stress. Methods: Hair cortisol levels were determined using the ELISA method (solid-phase enzyme-linked immunoassay, Alpco Diagnostics, Windham, N.H., USA) in 60 infants >25 weeks gestational age at birth. Results: No significant differences were found between the hair cortisol levels of term infants compared to preterm infants in the NICU. When compared to a group of healthy term infants, hospitalized infants had significantly higher hair cortisol levels (t (76) = 2.755, p = 0.004). A subgroup analysis of the term NICU infants showed a statistically significant association between total number of ventilator days and hair cortisol levels. For every extra day on the ventilator, hair cortisol levels increased on average by 0.2 nmol/g (p = 0.03). 21% of the variance in hair cortisol levels was explained by the total number of days on the ventilator. Conclusions: Hair cortisol is influenced by days of ventilation in NICU term infants. This is a potentially valid outcome for chronic neonatal stress in these infants and warrants further investigation.