ESPE Abstracts

Background: Low-dose adrenocorticotropic hormone stimulation test (LDST) is commonly used for evaluating the adequacy of hypothalamo-pituitary-adrenal axis functions. However, there is still no standardization between protocols used in different centres.

Objective: To contribute to the optimal time of highest cortisol response in the LDST in children.

Design: A prospective study of LDST resultsperformed on children with clinical suspicion of adrenal insufficiency.

Method: Cortisol concentrations were measured at baseline, 30, 40, and 60 minutes after intravenous administration of 1 μg tetracosactide. Basal cortisol levels were also assessed by using liquid chromatography-mass spectrometry (LC-MS/MS). Adrenal insufficiency was defined as a stimulated cortisol level <18.1 μg/dL (500 nmol/L).

Results: 135 patients (61girls, mean age 9.98±5.93 years) were included. Cortisol response was adequate at any time point in 80.7% (n=109) of patients. In the case of a single measurement after stimulation, 62.9% (n=85) of the patients had an adequate response at 30.th minute, 72.6% (n=98) at 40.th minute, and 70.4% (n=95) at 60 minute (P=0.04). In the case of one measurement at the 40.th minute, 8 patients (7.3%) who had an adequate response at 60.th minute, would have been misdiagnosed. In this condition, delta cortisol (0 to 40) value above 9.3 μg/dL reduces the probability of LDST result being false-negative by a negative predictive value of 95.5%. The threshold basal cortisol value predicting a negative LDST result in the immunoassay method was determined as >6.5 μg/dL (69.2% sensitivity/74.3% specificity) and >6.1 μg/dL (59.1% sensitivity/78% specificity) by LC-MS/MS method (P = 0.0001).

Conclusions: In the LDST, sampling at the 40th and 60th minutes after stimulation minimizes the false-positive LDSTs, and in the case of a single measurement, the 40.th minute sampling reduces false-negativity compared to the 30.th and 60.th minutes.