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 1 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. Copyright (c) 2007 S. Karger AG, Basel.