How should I interpret the results of a 17-hydroxyprogesterone (17-OHP) test in the context of suspected CAH?

Interpretation of 17-hydroxyprogesterone (17-OHP) in suspected congenital adrenal hyperplasia (CAH) requires understanding that elevated 17-OHP levels are a key biochemical marker indicating 21-hydroxylase deficiency, the most common cause of CAH.

In a suspected case, a significantly raised basal 17-OHP level strongly supports the diagnosis of classic CAH, especially if levels exceed the established diagnostic thresholds used in UK clinical practice ¹. However, borderline or mildly elevated basal 17-OHP levels may require an ACTH stimulation test to clarify diagnosis, as stimulated 17-OHP levels provide greater sensitivity and specificity for detecting partial enzyme deficiency or non-classic CAH ¹.

It is important to interpret 17-OHP results in the clinical context, considering age, sex, and timing of sample collection (ideally morning fasting samples), as physiological variations can affect levels ¹. Additionally, recent literature emphasizes that steroid profiling, including 17-OHP alongside other steroid precursors, can improve diagnostic accuracy and help differentiate CAH subtypes (Sarafoglou et al., 2023; Bacila et al., 2024).

In summary, a raised 17-OHP level is a critical diagnostic biomarker for CAH, but borderline results should prompt further dynamic testing and steroid profiling to confirm diagnosis and guide management ¹ (Sarafoglou et al., 2023; Bacila et al., 2024).