Accurate assessment of adrenal function is essential in patients with hypothalamic–pituitary–adrenal (HPA) disease. The measurement of salivary cortisol (SaC) instead of serum cortisol (SeC) offers several advantages, such as the determination of the free hormone. We evaluated the diagnostic value of SeC and SaC both unstimulated and during a high-dose short synacthen test (HDT) in comparison to the insulin tolerance test (ITT).
Comparative study between 2005 and 2007.
Fifty-five patients with HPA impairment and 21 healthy controls were enrolled. Samples were collected in the early morning and over 120 min during the HDT. Receiver operating characteristic analysis revealed individual thresholds for four HDT periods (0–30, 0–60, 0–90, and 0–120 min).
The ITT identified 30 subjects as adrenal insufficient. With respect to the four HDT periods, sensitivity and specificity were 67–79% and 71–88% for SeC, compared with 63–72% and 72–86% for SaC. If upper and lower thresholds (with specificities >95%) were applied, patients were diagnosed in 40–45% by SeC and in 25–31% by SaC. The combination of basal cortisol and HDT allowed a diagnosis in 47–49% (SeC) and in 42–45% (SaC) respectively.
We suggest the determination of basal SeC or SaC as first-line test. In comparison to the ITT, the HDT has only limited value in screening for alterations of the HPA axis. If the HDT is performed, sampling may be limited to 30 min post-synacthen, using either SeC or SaC. Due to the ease of collection and the independence of binding proteins, SaC may be preferable.