Determination of reference interval for midnight salivary cortisol among healthy adults in Kinta valley region

Cortisol has been well established as an assessment of adrenocortical function. Cortisol levels are elevated in Cushing’s syndrome and the levels are low in adrenal insufficiency such as Addison’s disease. The Endocrine Society Guidelines has recommended that screening for Cushing’s syndrome in adults includes assessment of Urinary Free Cortisol (UFC) , overnight dexamethasone suppression test and midnight salivary cortisol. Measurement of midnight salivary cortisol is the most sensitive, specific and non-invasive method for screening of Cushing’s syndrome. This study aims to establish reference interval of midnight salivary cortisol in healthy adults in Kinta Valley region. This cross-sectional study involving 125 participants. 86 (68.8%) females and 39 males (31.2%), median age = 19 (19-19) and median BM1 = 21.62 (19.40-24.77). Participants were refrained from teeth brushing, eating or drinking 1 hour prior to samples collection. Midnight salivary samples were taken using Saliva Bio Oral Swab (SOS) equipped with an insert containing oral swab for the analysis of midnight salivary cortisol on the Roche Cobas e620-analyzer (Germany) via electrochemiluminiscence immunoassay (ECLIA). The midnight salivary cortisol presented a non-Gaussian distribution with median [1QR] 2.2 (1.55, 3.45), 2.5th percentile (90 % Cl); 1.5 (1.5-1.5), 97.5th percentile (90 % CI); 12.6 (8.4-15.8). Our. study showed no association between gender and MSC [(n=125); p > 0.05, 90 (%) CI]. Spearman’s rank correlation analysis indicated that midnight salivary cortisol levels were significantly correlated with body mass index although it was a poor correlation (p=0.224, P < 0.05). Using the same statistical analysis, there is no correlation observed between midnight salivary cortisol levels and age (p=0.106, P=0.239). These findings contribute toward establishing the laboratory’s reference range for midnight salivary cortisol which can provide to the national’s reference range progra