The Low-Dose ACTH test: Usefulness of Combined Analysis of Serum and Salivary Maximum Cortisol Response in Paediatrics

CONTEXT: The low-dose (1 µg) ACTH test (LDT) is widely used to assess central adrenal insufficiency (CAI); however, the serum cortisol cutoff value is controversial. Salivary cortisol (SC) may be a more accurate measurement for CAI. OBJECTIVE: To assess a new maximum cutoff value of serum cortisol after LDT in pediatric patients, taking into account serum and SC measurements. DESIGN AND SETTING: Prospective study in a pediatric tertiary referral center. WORKING HYPOTHESIS: The combined analysis of serum and SC response to LDT might improve LDT for CAI diagnosis. PARTICIPANT AND OUTCOME MEASUREMENT: A total of 145 pediatric patients underwent LDT. Serum and SC levels were measured. A central adrenal sufficient (CAS) response was established according to the reference serum cortisol cutoff value of ≥497 nmol/L. RESULTS: The LDT study showed central adrenal sufficiency in 72 patients and CAI in 73 patients. Considering the lower quartile of maximum SC value (21 nmol/L) in the CAS group, an intermediate CAI (InCAI) group and a real CAI (RCAI) group were defined. Regarding the median maximum value of serum cortisol levels in the InCAI group, a new serum cortisol cutoff value of 450 nmol/L was established. Furthermore, 91% of the patients in the RCAI group were below this cutoff value. CONCLUSION: The combined evaluation of maximum serum and SC levels to LDT might be useful to define an InCAI group and to avoid unnecessary hormone replacement therapy. However, rigorous patient follow-up is required.