The Low-Dose ACTH Test: Usefulness of Combined Analysis of Serum and Salivary Maximum Cortisol Response in Pediatrics.

Abstract

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. To assess a new maximum cutoff value of serum cortisol after LDT in pediatric patients, taking into account serum and SC measurements. Prospective study in a pediatric tertiary referral center. The combined analysis of serum and SC response to LDT might improve LDT for CAI diagnosis. 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. 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. 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.