Timing of 17-hydroxyprogesterone measurement during the standard-dose Synacthen test in pediatric patients evaluated for non-classical congenital adrenal hyperplasia due to 21-hydroxylase deficiency.

OBJECTIVE: We aimed to evaluate the diagnostic utility of the 30-minute 17-hydroxyprogesterone (17-OHP) measurement during the standard-dose Synacthen test. SUBJECTS AND METHODS: This retrospective study analyzed the medical records of patients aged 0-18 years who underwent Synacthen testing for suspected non-classical congenital adrenal hyperplasia due to 21-hydroxylase deficiency between 2000 and 2024. RESULTS: Among 150 patients included, the median age was 13 years (range 5.5-18), and 85.3% were female. Twenty-nine patients exhibited a peak stimulated 17-OHP level ≥ 10 ng/mL. In three of these patients, the 30-minute 17-OHP level was within normal limits, whereas all had diagnostic 17-OHP levels at 60 minutes. No patients exhibited a diagnostic 17-OHP level at 30 minutes with a non-diagnostic value at 60 minutes. Using a basal 17-OHP cut-off value of 3.78 ng/mL, sensitivity and specificity were 89.7% and 94.2%, respectively. The V281L variant was the most frequently identified pathogenic variant. CONCLUSION: The 60-minute 17-OHP measurement demonstrated greater diagnostic sensitivity than the 30-minute measurement in this cohort and may provide adequate diagnostic information in pediatric patients evaluated for non-classical congenital adrenal hyperplasia, as no additional cases were identified exclusively at the 30-minute time point.