Assessment of perturbations in the circadian rhythm of cortisol secretion provides a measure of the hypothalamic-pituitary-adrenal axis (HPA) function, including responses to exogenous glucocorticoids. Salivary cortisol sampling allows testing of free serum cortisol among ambulatory subjects. We assessed this approach in the study of adults with asthma and rhinitis.
We analyzed data from an ongoing, prospective cohort study of adults with asthma or rhinitis. Subjects were asked to collect two saliva samples: thirty minutes after awakening (AM) and 12 hours later (PM). Subjects placed a cotton swab under the tongue for two minutes. After home freezing, samples were later collected and stored at -20 C. until assayed for salivary cortisol using a high-sensitive enzyme immunoassay (Salimetrics, PA). The test has a lower limit of sensitivity of 0.19 nmol/l. We used the Wilcoxon rank sum to compare the differences in AM and PM cortisol levels by type of corticosteroid used.
We analyzed data for 153 subjects (126 with asthma; 27 with rhinitis alone). The mean age was 45±9 years; 105 (69%) were female. Among subjects using inhaled or systemic corticosteroids in the previous 2 weeks, AM cortisol values were lower (n=62; 8.8±5.8 nmol/l) compared to all others (n=91; 11.0±6.5; p=0.04). Excluding 8 subjects on oral glucocorticoids narrowed the difference (inhaled steroid AM cortisol=9.4±5.7; p=0.17). Within the inhaled glucocorticoid group, 39 subjects used fluticasone, while 15 used other steroid types. AM values were somewhat lower in the fluticasone group (8.7±5.1 v. 11.4±6.9; p=0.2), while PM values were statistically lower (1.5±1.0 v. 1.9±0.8; p=0.03).
This report shows that (1) salivary cortisol can be used to assess HPA function in ambulatory adults with asthma or rhinitis (2) HPA suppression due to exogenous steroid can be detected, confirming the validity of the sampling (3) the methodology is sensitive enough to detect effects of different glucocorticoid formulations.
Inhaled steroids, particularly highly lipid soluble forms such as fluticasone, can have detectable effects on the HPA axis.
P.D. Blanc, None.