In congenital adrenal hyperplasia due to 21-hydroxylase deficiency, which lab finding is expected?

In congenital adrenal hyperplasia (CAH) due to 21-hydroxylase deficiency, the enzymatic block prevents the conversion of 17-hydroxyprogesterone (17-OHP) to cortisol and aldosterone. As a result, there is an accumulation of 17-OHP in the adrenal glands and subsequently in the blood. This increased level of 17-hydroxyprogesterone is a hallmark laboratory finding in this condition and serves as a key diagnostic criterion for CAH.

The deficiency in 21-hydroxylase leads to decreased production of cortisol and aldosterone, which in turn results in increased adrenocorticotropic hormone (ACTH) secretion due to ineffective feedback inhibition. The continued stimulation of the adrenal cortex by ACTH drives the production of steroid precursors that cannot be adequately converted, thereby leading to elevated levels of 17-OHP.

In the context of other findings, cortisol levels would be low due to the blockade in its synthesis, and adrenal androgens may be elevated, not decreased, due to shunting of steroid precursors toward the androgen pathway. This cascade of hormonal imbalance elucidates the expected laboratory finding of increased 17-hydroxyprogesterone in patients with 21-h