Diagnostic cut-offs of 17-hydroxyprogesterone by LC-MS/MS in children with non-classical congenital adrenal hyperplasia.

Purpose: Congenital adrenal hyperplasia (CAH) is an autosomal recessive disorder, commonly caused by 21-hydroxylase mutations, that converts 17-hydroxyprogesterone (17-OHP) into 11-deoxycortisol in the adrenal cortex. Elevated morning serum levels of 17-OHP identify suspected CAH, and the diagnosis is confirmed by CYP21 A2 gene analysis. Liquid-chromatography tandem mass spectrometry (LC-MS/MS) has become the recommended method for 17-OHP measurement; however, diagnostic 17-OHP thresholds measured with LC-MS/MS are not yet defined. We aimed to identify optimal cut-offs for basal and peak 17-OHP levels after ACTH stimulation test, measured by LC-MS/MS, to distinguish non-classical CAH (NC-CAH) and heterozygous carriers (HC) from wild type subjects (WT) in children.

Methods: We retrospectively analyzed the records of 198 children referred for suspected NC-CAH.

Results: The ideal basal 17-OHP cut-off to differentiate NC-CAH from WT subjects was 0.94 ng/mL (2.82 nmol/L) with AUC 0.988 (95% CI 0.972-1.000; sensitivity 100%, specificity 90%). The optimal peak 17-OHP cut-off was 7.81 ng/mL (23.43 nmol/L) with AUC 0.998 (95% CI 0.994-1.000; sensitivity 100%, specificity 97%). The ideal basal 17-OHP cut-off to distinguish HC from WT subjects was 0.81 ng/mL (2.43 nmol/L), with AUC 0.727 (95% CI 0.645-0.809; sensitivity 54%, specificity 83%); while the optimal peak 17-OHP cut-off was 3.79 ng/mL (11.37 nmol/L) with AUC 0.932 (95% CI 0.894-0.971; sensitivity 96%, specificity 87%).

Conclusions: The ideal cut-offs of peak 17OHP able to distinguish NC-CAH and HC individuals from WT subjects were significantly lower to using LC-MS/MS. These new thresholds demonstrate high sensitivity and specificity, making them effective in distinguishing individuals with suspected NC-CAH.