Salivary Cortisol and Cortisone After Low-Dose Corticotropin Stimulation in the Diagnosis of Adrenal Insufficiency

Ingrid Yin Fung Mak; Benjamin Yick Toa Au Yeung; Ying Wai Ng; Cheung Hei Choi; Heidi Yan Ping Iu; Chi Chung Shek; Sau Cheung Tiu

Disclosures

J Endo Soc. 2017;1(2):96-108. 

In This Article

Results

Fifty-six healthy Chinese volunteers (28 males and 28 females; mean age, 37 years; age range, 18 to 66 years) were recruited. Two subjects were taking amlodipine for hypertension; 1 subject was taking metformin for diabetes mellitus; and 1 subject was taking amlodipine, losartan, metformin, simvastatin, and aspirin for hypertension, hyperlipidemia, and diabetes. All others had no chronic medical illnesses and required no medication within 1 month of testing. All of them had normal liver, renal, and thyroid function tests. Their mean basal and peak serum total cortisol levels were 252.8 ± 78.5 and 509.2 ± 66.6 (501.6 for males and 516.8 for females) nmol/L, respectively ( Table 1 ); 96.4% (n = 54) of them reached peak cortisol levels at 30 minutes after Synacthen injection. The mean CBG of the male and female volunteers were 28.5 ± 3.3 and 32.9 ± 4.3 μg/mL, respectively. The distribution of serum cortisol and CBG was shown to be normal. The value corresponding to the mean − 2 SDs of the peak serum cortisol in this healthy cohort (376 nmol/L) was used as the gold standard to further evaluate the salivary parameters in the patient group ( Table 1 ).

One hundred seventy-one Chinese patients (82 males and 89 females; mean age, 57 years; age range, 19 to 89 years) completed the study. They were referred for investigation of AI due to the following reasons: nonspecific clinical features (n = 55) such as unexplained dizziness and fatigue, electrolyte disturbance (n = 18) such as hyponatremia, diseases or interventions involving the sellar and suprasellar regions (n = 124), previous administration of exogenous glucocorticoids (n = 32), and postadrenalectomy (n = 4) ( Table 2 ). One hundred sixty (93.6%) of them reached their peak cortisol levels at 30 minutes after Synacthen injection. Patients with peak serum cortisol < 376 nmol/L were classified as having AI; the rest were classified as non-AI. The mean peak serum cortisol for the AI group (n = 59) was 203.2 ± 121.6 nmol/L, whereas that for the non-AI group (n = 112) was 486.8 ± 76.7 nmol/L ( Table 2 ).

The mean basal and peak salivary cortisol levels of the healthy subjects were 4.3 ± 2.6 and 23.9 ± 8.5 nmol/L, respectively ( Table 1 ). The mean basal and peak salivary cortisol levels for the AI patients were 2.0 ± 2.1 and 5.9 ± 6.9 nmol/L, respectively, whereas those for the non-AI patients were 4.7 ± 3.0 and 20.9 ± 10.1 nmol/L, respectively ( Table 2 ).

From the ROC curve analysis (Fig. 1), peak salivary cortisol had a larger area under the curve (AUC) (0.914 ± 0.026; estimate ± standard error) than did basal salivary cortisol (0.836 ± 0.036) ( Table 3 ). For the highest accuracy, the cutoff values of peak and basal salivary cortisol were 8.6 nmol/L [sensitivity 84.7%, specificity 94.6%, positive likelihood ratio (LR+) 15.82, negative likelihood ratio (LR−) 0.16] and 1.7 nmol/L (sensitivity 62.7%, specificity 95.5%, LR+ 14.05, LR− 0.39), respectively.

Figure 1.

ROC curves of basal serum cortisol, salivary cortisol, and salivary cortisone, and post-LDSST peak salivary cortisol and cortisone in the patient group (n = 171) when AI (disease) was defined as post-LDSST serum cortisol < 376 nmol/L.

An alternative approach for establishing the cutoff value for salivary cortisol is to derive it from the results of healthy subjects. The 2.5th percentile of the peak salivary cortisol values in the healthy subjects was 10.9 nmol/L ( Table 1 ). However, the values were not normally distributed due to a subject whose serum cortisol, salivary cortisol, and cortisone (at 0/30/60 minutes) were 236/624/494, 3.6/55/33, and 22/112/88 nmol/L, respectively (i.e., she had a greater response to LDSST than did other subjects). This was a healthy 18-year-old female with an estimated glomerular filtration rate of 102 ml/min/1.73 m2, a normal thyroid function test, an albumin level of 53 g/L, and a CBG of 32.2 μg/mL. After the exclusion of this single outlier,[25] the results of the remaining 55 healthy volunteers became normally distributed, and the reference value for peak salivary cortisol (mean − 2 SDs) became 8.4 nmol/L ( Table 1 ), which is very close to the value of 8.6 nmol/L derived from the ROC curves of the patient group using as a reference standard their peak serum cortisol response to LDSST.

The mean basal and peak salivary cortisone levels of the healthy volunteers were 25.4 ± 10.4 and 60.3 ± 13.3 nmol/L, respectively ( Table 1 ). The mean basal and peak salivary cortisone levels for the AI patients were 9.6 ± 9.8 and 18.9 ± 16.2 nmol/L, respectively, whereas the values for the non-AI patients were 24.5 ± 10.5 and 54.0 ± 17.3 nmol/L, respectively ( Table 2 ).

Peak salivary cortisone also had a larger AUC (0.926 ± 0.022) than did basal salivary cortisone (0.862 ± 0.033) from the ROC curve analysis (Fig. 1; Table 3 ). For the highest accuracy, the cutoff values of peak and basal salivary cortisone were 33.5 nmol/L (sensitivity 84.7%, specificity 88.4%, LR+ 7.30, LR− 0.17) and 12.5 nmol/L (sensitivity 72.9%, specificity 88.4%, LR+ 6.28, LR− 0.31), respectively. As for salivary peak cortisol, an alternative approach to establishing the cutoff value for salivary cortisone is to derive it from the results of the healthy subjects. The 2.5th percentile of the peak salivary cortisone values in all the healthy subjects studied was 37.1 nmol/L ( Table 1 ). However, the values were not normally distributed due to the outlier mentioned previously. After the exclusion of this single outlier, the results of the remaining 55 healthy volunteers became normally distributed, and the reference value for peak salivary cortisol (mean – 2 SDs) became 36.5 nmol/L, which is very close to the 33.5 nmol/L derived from the ROC curves of the patient group.

The correlation coefficients (r) between peak salivary cortisol and cortisone with the peak serum total cortisol levels were 0.779 and 0.852, respectively (Fig. 2). Salivary cortisone had a better and more linear correlation with serum total cortisol, whereas salivary cortisol rose exponentially after serum cortisol level reached 400 to 600 nmol/L.

Figure 2.

Correlation between peak serum cortisol with (A) peak salivary cortisol and (B) peak salivary cortisone in all subjects (n = 227) (r = 0.779 and 0.852, respectively; P < 0.01).

Figure 1 and Table 3 illustrated that the ROC for all basal tests yielded significantly smaller AUC with lower sensitivity and specificity at all cutoff values than the peak values. Basal serum cortisol had the highest AUC (0.903 ± 0.024) among all basal tests, with the optimal cutoff value at 170 nmol/L (sensitivity 76.3%, specificity 88.4%, LR+ 6.57, LR− 0.27). The best cutoff values for basal salivary cortisol and basal salivary cortisone were 1.7 nmol/L (sensitivity 62.7%, specificity 95.5%) and 12.5 nmol/L (sensitivity 72.9%, specificity 88.4%), respectively ( Table 3 ).

Eighteen patients (10.5%) were found to have discordant serum and salivary (cortisol and/or cortisone) results: 9 of them were classified as "AI" by the peak serum cortisol criteria (Supplemental Data 2), and the other 9 "non-AI" (Supplemental Data 3). Five subjects among the AI patients had low CBG levels of 13.0 to 21.6 μg/mL and non-AI salivary results, and only 1 non-AI subject had a higher CBG level of 45.0 μg/mL and AI salivary results. Five subjects were on oral estrogen therapy. We did not observe any discrepancy between their serum and saliva results (Supplemental Data 4).

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