Usefulness of salivary cortisol as a marker of secondary adrenal insufficiency in paediatric patients

Abstract

Background: The main cause of adrenal insufficiency (AI) in paediatric patients is prolonged treatment with corticosteroids. Determination of plasma cortisol (PC) during ACTH test is the most used adrenal function indicator in clinical practice. However, determination of salivary cortisol (SC), a simple test especially useful in children in order to avoid invasive procedures, can be used as an alternative technique for the diagnosis of adrenal disease. Methods: A two-year prospective study (January 2014-January 2016) in paediatric patients (2-18 years of age) treated with corticosteroids for more than fifteen days, who were investigated for suspected AI. Low-dose ACTH test was used to determine adrenal function and samples for SC and PC were obtained simultaneously in basal situation and during the test (at 30, 60 and 90 minutes). Results: 230 samples (118 PC-112 SC) of 30 studies belonging to 20 patients (4 males), mean age 10.93 years ± 3.69 SD. Pearson’s correlation coefficient showed a positive correlation between PC and SC (r = 0.618, p < 0.001). All the studies with some determination of PC higher than 18 μg/dL (n = 8) had a SC peak higher than 0.61 μg/dL with a specificity of 66.67% and a sensitivity of 93.94% (ROC analysis). Conclusion: Measurement of SC is a less invasive, easier and quicker test than PC to measure plasma free cortisol levels. In our study, a SC peak in low-dose ACTH test higher than 0.61 μg/dL was able to discriminate patients without AI, and proved to be a useful tool in the initial evaluation of children with suspected AI.