Comparison of salivary cortisol and calculated free plasma cortisol during low-dose ACTH test in healthy subjects

ObjectivesTo compare free plasma cortisol (FPC) with salivary and calculated cortisol.Design and methodsFPC, salivary cortisol, free cortisol index (FCI), albumin-derived free cortisol index (FCIalb), Coolen's and Dorin's cortisol were assayed during repeated low-dose ACTH test in healthy women.ResultsFPC significantly correlated with its surrogates, the most with FCIalb and salivary cortisol. FPC and salivary cortisol showed the highest method agreement.ConclusionsFCIalb and salivary cortisol are preferred surrogates of FPC.