Can salivary cortisol be used in diagnosing adrenal insufficiency during the acute and subacute phases of traumatic brain injury?

Introduction: The diagnosis of adrenal insufficiency (AI) related to traumatic brain injury (TBI) remains a challenge. We investigated the basal and low-dose adrenocorticotropic hormone (ACTH)-stimulated serum cortisol and salivary cortisol (SaC) levels and the diagnostic utility of SaC levels during 28 days following TBI.

Materials and methods: Blood samples were collected for basal levels [sequentially from day 1 (D1) to D7 and on D28)] and for peak serum cortisol and SaC responses to the low-dose ACTH stimulation test (on D1, D7, and D28). After the patient enrollment period was completed, patients were retrospectively categorized as AI or AS (adrenal sufficiency) for each day separately, based on a basal serum cortisol cut-off level of 11 µg/dL, and data analysis was performed between the groups.

Results: Thirty-seven patients and 40 healthy controls were included. Median basal serum cortisol levels were higher in patients on D1 but were similar on other days. Median basal SaC levels were higher in patients on D1 and D2 but were similar on other days. Median peak serum cortisol and SaC levels were similar on D1 but were lower in patients on D7 and D28. Median basal SaC levels were higher in the AS group than in the AI group on all days.

Discussion and conclusions: When evaluating AI during the course of TBI, the cut-off for basal SaC levels is 0.5-0.6 µg/dL throughout the first week, except for 1.38 µg/dL on D2. SaC levels may serve as a surrogate marker for accurately reflecting circulating glucocorticoid activity.