OR30-02 Salivary Cortisol Response To The High Dose ACTH Stimulation Test Provides A Reliable Alternative To Serum Cortisol Measurement In The Evaluation of Suspected Hypoadrenalism, And Is Unaffected By Cortisol-Binding Concentration

Disclosure: N. El-Farhan: None. S. Rees: None. S. Tennant: None. C. Evans: None. A. Rees: None. Context The serum total cortisol response to the ACTH stimulation test is widely used to assess adrenocortical function but is affected in conditions of altered cortisol-binding globulin (CBG) concentration. Salivary cortisol reflects free cortisol concentrations and may offer a reliable alternative. Objectives: 1. To establish the salivary cortisol response to the high dose ACTH stimulation test in healthy volunteers and in patients with altered CBG concentrations. 2. To evaluate the performance of a lower reference limit (LRL) determined in healthy volunteers in patients with suspected hypoadrenalism. Design: A high dose (250 µg) intravenous ACTH stimulation test was undertaken in 139 (60 male, 79 female) healthy volunteers, 24 women taking an oestradiol-containing oral contraceptive pill (OCP females), 10 patients with low serum protein concentration secondary to the nephrotic syndrome or liver cirrhosis (LP patients) and 29 patients with suspected hypoadrenalism (SH patients). Salivary cortisol was measured by liquid chromatography-tandem mass spectrometry. The mean and estimated LRL of the 30-minute salivary cortisol response to ACTH stimulation (mean - 1.96 SD) were derived from log-transformed concentrations. The LRL was subsequently applied as a diagnostic cut-off in SH patients. Results: CBG concentrations were 58 [42-81] mg/L), 64 mg/L [43-95], 41 [28-60] mg/L and116 [84-159] mg/L in male volunteers, female volunteers, LP patients and OCP females, respectively. The mean 30-minute salivary cortisol concentration was 19.3 [2.5(th)-97.5(th) percentile 10.3-36.2] nmol/l in healthy volunteers, with no difference between genders. Corresponding values were not different in OCP females (19.7 [9.5-41.2] nmol/l; p=0.59) and LP patients (19.0 [7.7-46.9] nmol/l; p=0.97), in contrast to 30-minute mean serum cortisol responses which differed between healthy female volunteers (555 [421-731] nmol/l) and OCP females (869 [649-1162] nmol/l; p<0.001). Overall diagnostic agreement between 30-minute salivary and serum responses in patients undergoing evaluation for SH was high (79%). Conclusions: Salivary cortisol response to intravenous ACTH stimulation offers a reliable alternative to serum cortisol measurement in the assessment of patients with suspected hypoadrenalism and may be especially useful in conditions of altered CBG concentration. Presentation: Sunday, June 18, 2023