21-Deoxycortisone: A Novel Sensitive and Specific Newborn Screening Marker for Congenital Adrenal Hyperplasia

21-deoxycortisol is a sensitive and specific blood marker for congenital adrenal hyperplasia (CAH). We postulated that 21-deoxycortisone, the 11β-hydroxysteroid dehydrogenase metabolite of 21-deoxycortisol, may also be an accurate bloodspot marker of CAH. Measurement of 21-deoxycortisone was performed on 42 residual NBS specimens with a true positive result for CAH, 11 with a false negative result, and 439 specimens with a false positive result. For this study, the test was considered positive if 21-deoxycortisone was detected. The sensitivity and specificity of 21-deoxycortisone as a marker for classical CAH was calculated and compared to 21-deoxycortisol data from a previous New Zealand study. The method for 21-deoxycortisone measurement was linear to 1000 nmol/L and precision was 7.3–10.3%. The lower limit of quantification was 2 nmol/L, and recovery was 99%. 21-deoxycortisone was ≥2 nmol/L in all 42 true positive samples and in 10 false negative samples, and was not detected in the false positive group of specimens. The sensitivity of 21-deoxycortisone was 98.1%, and specificity was 100%. In a previous study, the sensitivity of 21-deoxycortisol was 88.7% and specificity was 99.8% in 1910 newborn screening tests carried out between 2018 and 2021. Incorporating 21-deoxycortisone into a second-tier test and adjustment of primary screening protocols could improve the accuracy of newborn screening for CAH. Longer term prospective studies on the performance of 21-deoxycortisone are warranted.