Comparison of cortisol samples in the first two weeks of life in preterm infants.

BACKGROUND Growing literature on negative childhood stress emphasizes the need to understand cortisol values from varying biomarker samples. OBJECTIVE This work aimed to examine cortisol samples for usability, associations, and individual stability in neonates. SUBJECTS The sample consisted of preterm infants (n=31). MATERIALS AND METHODS Analyses on cortisol collected from cord blood and from saliva and urine samples on days 1, 7, and 14 included Spearman correlations and paired t-tests. RESULTS Usability rates were 80.6% (cord blood), 85.9% (saliva), and 93.5% (urine). Salivary and urinary cortisol levels had significant correlation on day 1 only (p=0.004). Significant differences in individual stability of cortisol concentrations existed except in urine on days 1 and 7 and in saliva on days 7 and 14. CONCLUSIONS Usability was highest for urine samples. We found little correlation between cortisol sample levels at each time; individual stability of cortisol concentrations was minimal. Interpretation of cortisol findings in all studies should be performed cautiously.