Is the Correlation between Salivary Cortisol and Serum Cortisol Reliable Enough to Enable Use of Salivary Cortisol Levels in Preterm Infants?
Newborn premature infants are susceptible to development of relative adrenal insufficiency following transition from fetal to extrauterine life. However, the best diagnostic test for adrenal insufficiency in neonates has yet to be developed.Objectives and Methods
The aim of this study was (1) to assess the feasibility of obtaining sufficient saliva sample to allow measurement of cortisol by liquid chromatography coupled to tandem mass spectrometry and (2) to assess the correlation, if any, between salivary and serum cortisol in preterm infants of ≤32 weeks’ gestational age at birth.Results
Samples for 230 paired serum and saliva cortisol levels from 90 preterm infants were analyzed. 87.5% of samples collected had sufficient salivary volumes for measurement. Despite being statistically significant (p < 0.0001), the correlation (Spearman r = 0.674) between serum and salivary cortisol was not strong.Conclusion
Salivary free cortisol measurement is feasible but cannot be used to accurately reflect serum total cortisol. Further studies comparing salivary free cortisol to serum free cortisol and establishing normative data are needed before salivary cortisol can be used for diagnostic purposes.