IMPE Abstracts

Background: Non-classical congenital adrenal hyperplasia (NC-CAH) by variants in the CYP21A2 gene, cause a deficiency in the enzyme 21α-Hydroxylase and accumulation of precursors proximal to the blockage (progesterone and 17-hydroxyprogesterone- 17OHP), and androgen production. 17-OHP levels below 2ng/dl rule out the alteration, while levels above 10ng/dl confirm the diagnosis. Levels between 2-10 ng/dl require ACTH stimulation testing. However, the ACTH ampoule is expensive and not available in some medical settings. Identifying the ideal cut-off point for basal 17-OHP levels with the most appropriate sensitivity and specificity, bypasses unnecessary ACTH stimulation testing and reserves its use for cases with a higher pretest probability.

Objective: To identify the cut-off point of basal 17-hydroxyprogesterone levels for ACTH stimulation testing, in patients with suspected non-classical congenital adrenal hyperplasia.

Methods: Diagnostic accuracy study. Univariate analysis of demographic characteristics and basal and post-stimulation 17-hydroxyprogesterone levels. Spearmann correlation index. Calculating the ROC curve to identify the cut-off point with the ideal sensitivity and specificity.

Results: The average patient age was 15.43 years (±11.01). 71.67% were older than 18. 82.32% were female. The median basal 17OHP level was 1.24ng/dl (RIC 1.19). After ACTH stimulation, the median was 2.85ng/dl (RIC 2.44). The median basal 17 OHP level in those under 18 was 1.32 (RIC 0.99), and 1.21ng/dl (RIC 1.24) in those above 18. There were no statistically significant differences between the age groups (P=0.19). After ACTH stimulation, median basal 17OHP levels in those younger than 18 was 2.66ng/dl (RIC 2.1), and 2.92 (RIC 2.5) in those older than 18. There were no statistically significant differences between the age groups (P=0.35). The Spearmann correlation between basal 17OHP vs post-ACTH stimulation was 0.65 (P=0.000). The cutoff point of 4.4ng/dl had a sensitivity of 90.91% and a specificity of 96.84% for the diagnosis of NC-CAH, and isolated non-classical adrenal hyperplasia in the 97.0% of cases (95% CI 91.1%-99.4%). The cut-off's Youden value was 0.92.

Conclusion: Basal 17OHP levels greater than 4.4ng/dl can isolate patients with non-classical congenital adrenal hyperplasia in 97% of cases with high sensitivity and specificity.