Which steroid does not affect the measurement of cortisol levels?

The measurement of cortisol levels can be influenced by various glucocorticoids, leading to altered results in clinical assessments. Dexamethasone is a synthetic glucocorticoid that is highly selective for the glucocorticoid receptor and has minimal mineralocorticoid activity. This characteristic makes it less likely to interfere with the endogenous cortisol production and measurement since it is not converted into active cortisol metabolites.

While hydrocortisone, prednisone, and betamethasone can affect cortisol levels, either through feedback inhibition of the hypothalamic-pituitary-adrenal (HPA) axis or by their conversion into active forms, dexamethasone maintains a more stable profile in this regard. When dexamethasone is administered, it is less likely to stimulate the HPA axis as significantly as the other steroid options, thus allowing for more accurate cortisol measurements.

Therefore, in the context of measuring cortisol levels, dexamethasone is the steroid that does not lead to significant alterations, making it the correct answer.