The clinical applications of salivary cortisol measurements were evaluated by radioimmunoassay of time-matched saliva and plasma samples. Salivary cortisol levels of normal subjects exhibited a significant (p less than 0.001) diurnal variation with a mean (+/- SD) concentration of 8.7 +/- 4.8 nmol/L at 0800-1000 h and 2.4 +/- 1.1 nmol/l at 1500-1700 h. After an overnight dexamethasone suppression test, morning salivary cortisol levels decrease to 2.7 +/- 0.7 nmol/L (p less than 0.001 vs normal). An excellent correlation (r = 0.805) of cortisol measurements with time-matched saliva and plasma samples was obtained (y = 0.03x + 0.88, p less than 0.001, n = 91). Hypercortisolism was confirmed by raised salivary cortisols in only half of patients with elevated total plasma levels, thereby indicating that salivary cortisol measurements is a better index of adrenal status.
Since conventional radioimmunoassays (RIA) for measurement of 17-hydroxyprogesterone (17-OHP) in serum samples require a laborious solvent extraction step, a direct and rapid in-house RIA was developed for early diagnosis and management of congenital adrenal hyperplasia (CAH). In-house rabbit anti-17-OHP antiserum, tritium labelled 17-OHP and dextran-coated charcoal were used in assay buffer with low pH 5.1 and preheated serum samples. Both inter- and intra-assay CVs were < 10% and the sensitivity was 1.2 nmol/l or 12 fmol/tube. Results from the direct assay correlated well with values from an extraction assay, r = 0.88 in samples from CAH patients, r = 0.85 in adults and children, 0.69 and 0.40 in term and preterm neonates respectively, 0.66 and 0.63 in luteal phase and third trimester pregnancy; p < 0.001 in all groups except p < 0.05 in preterm neonates. However, results from the direct assay were two to three times higher in serum samples from CAH patients, normal adults and children, but were five to seven times higher in pregnancy and term neonates and thirty times higher in preterm neonates. The markedly elevated levels measured by the direct assay are probably due to cross-reactivities with water-soluble steroid metabolites such as 17-hydroxypregnenolone sulphate and dehydroepiandrosterone sulphate (DHEAS). Although the direct assay is only useful as a screening test for preterm babies, it can be used for both diagnosis and monitoring of treatment of CAH in all other age groups.