Salivary cortisol as a tool for physiological studies and diagnostic strategies

Salivary cortisol is an index of plasma free cortisol and is obtained by a noninvasive procedure. We have been using salivary cortisol as a tool for p hysiological and diagnostic studies, among them the emergence of circadian rhythm in preterm and term infants. The salivary cortisol circadian rhythm in term and premature infants was established between 8 and 12 postnatal we eks. In the preterm infants the emergence of circadian rhythm was parallel to the onset of sleep rhythm, We also studied the use of salivary cortisol for screening for Cushing's syndrome (CS) in control and obese outpatients based on circadian rhythm and the overnight 1 mg dexamethasone (DEX) suppre ssion test. Salivary cortisol was suppressed to less than 100 ng/dl after 1 mg DEX in control and obese patients. A single salivary cortisol measureme nt at 23:00 h and again after 1 mg DEX above the 90th percentile of the obe se group Values had sensitivity and specificity of 93 and 93% (23:00 h), an d 91 and 94% (after DEX), respectively. The sensitivity improved to 100% wh en we combined both parameters. We also studied 11 CS children and 21 age-m atched primary obese children for whom salivary cortisol sensitivity and sp ecificity were 100/95% (23:00 h): and 100/95% (1 mg DEX), respectively. Sim ilar to adults, sensitivity and specificity of 100% were obtained by combin ing 23:00 h and I mg DEX, The measure ment of salivary cortisol is a useful tool for physiological studies and for the diagnosis of CS in children and adults on an outpatient basis.