While 17α-hydroxyprogesterone with or without ACTH stimulation is the main marker for 21-hydroxylase deficiency, other markers have been proposed, with various degrees of acceptance: 21-Deoxycortisol is elevated in 21-hydroxylase deficiency. However, it is not elevated in preterm infants or in other forms of congenital adrenal hyperplasia. Unlike 17α-hydroxyprogesterone, 21-deoxycortisol is not produced in the gonads and is uniquely adrenal-derived. Consequently, 21-deoxycortisol it is a more specific marker of the 21-hydroxylase deficiency than 17α-hydroxyprogesterone. Even so, 21-deoxycortisol measurement has not been commonly performed by laboratories until 2019. Still, 21-deoxycortisol can be a key screening marker for 21-hydroxylase deficiency in newborn screening. 21-Deoxycorticosterone, also known as 11β-hydroxyprogesterone (11β-OHP), have been proposed as a marker in 1987. A study in 2017 has shown that in subjects with 21-hydroxylase deficiency, serum 11β-OHP concentrations range from 0.012 to 3.37 ng/mL, while in control group it was below detection limit of 0.012 ng/mL. This marker did not gain acceptance as of 2020 due to the fact that the test for the levels of this steroid is not routinely offered by diagnostic laboratories. Progesterone levels are higher in CAH subjects. A study has revealed that serum progesterone concentrations in boys (10 days to 18 years old) with 21-hydroxylase deficiency reached levels up to 10.14 ng/mL, i.e. similar to female luteal values, while in the control group of boys average level was 0.07 ng/mL (0.22 nmol/L), with values ranging from 0.05 to 0.40 ng/mL. The authors of the study propose to use progesterone as an additional marker for 21-hydroxylase deficiency. The study shows that the progesterone levels in CAH and non-CAH females are the same as in CAH and non-CAH males respectively – it is the condition that affects progesterone levels, not the sex, but for women between menarch and menopause, progesterone should be measured in days 3–5 of the cycle to have diagnostic value – the same condition also applies for 17α-hydroxyprogesterone. The specificity of progesterone as a marker of 21-hydroxylase deficiency, as opposed to deficiency of other enzymes involved in steroid pathways, was not well studied as of 2020. Cortisol is one of the two main final products of 21-hydroxylase, and the deficiency of this enzyme may lead to a certain degree of cortisol deficiency. Cortisol levels are lower in CAH subjects, on average, however, in milder cases cortisol levels can be normal, but as of 2020, this has not been yet well studied. Cortisol measurement