ESPE Abstracts

Background: Low-dose adrenocorticotropic hormone stimulation test (LDST) is widely used to assess patients for adrenal insufficiency. However, the predictive power of basal cortisol for the performance of LDST is not clear.

Objective: To determine the appropriate basal serum cortisol cutt-off values that predict a positive or negative LDST.

Design: A single-centre retrospective study to investigate LDSTs measuring baseline, 40th and 60th min cortisol concentrations after intravenous administration of 1 μg of synthetic ACTH.

Method: All the LDSTs of patients suspected of AI between November 2016 and February 2022 were included. A positive LDST (suggesting AI) was defined as a stimulated peak cortisol level <18.1 μg/dL (500 nmol/L). The associations between serum basal and peak cortisol levels in LDST were analysed and the diagnostic precision of basal serum cortisol concentrations for LDST performance was evaluated by ROC analysis.

Results: A total of 646 LDSTs performed on 537 (237 girls, median age 9.2±5.8 years) patients were evaluated. 215 LDSTs (33.3%) failed to show adequate cortisol response. Diagnoses leading to the use of LDST were: history of pituitary tumour, cranial radiotherapy or neurosurgery (n=94, 17.5%); presence of one or more pituitary hormone deficiencies (n=287, 53.5%); history of exogenous long-term glucocorticoid use (n=99, 18.4%); and clinical suspicion of AI (n=57, 10.6%). In the group that passed the LDST (n=431, 66.8%) the mean basal cortisol was 9.9±4.7 μg/dL (273±129.6 nmol/L); in the failed group (n=214, 33.2%) was 6.0±3.7 μg/dL (165.5±102 nmol/L) (P<0.0001). The mean basal ACTH level was 28.0±22.0 pg/ml in the passed group and 30.0±26.0 pg/ml in the failed group and this relationship is statistically insignificant (P=0.3089). The threshold basal cortisol value predicting a negative LDST result was determined as >6.8 μg/dL (189.5 nmol/L), having a sensitivity of 70%. Values above this threshold had a negative predictive value of 82.3%.

Conclusions: As a result of this unique study with large sample size carried out on a pediatric population, we determined serum basal cortisol of > or ≤6.8 μg/dL that can be used to confirm or exclude adrenal Insufficiency (AI) less invasively. Assessment of basal cortisol can reduce the need for LDST and can save cost and time.