Clinical Chemistry Numericals Practice Test 2026 - Free Clinical Chemistry Practice Questions and Study Guide

In ectopic ACTH production, the source of ACTH is outside the pituitary, so ACTH remains high and drives the adrenal glands to make excess cortisol. Because the ectopic source is not under the normal feedback control, giving high-dose dexamethasone does not shut off ACTH release or cortisol production. The result is that cortisol stays elevated despite the high-dose dexamethasone, i.e., the test is unsuppressed. So the pattern you’d expect is high cortisol, high ACTH, and unsuppressed cortisol with high-dose dexamethasone. This differentiates it from pituitary Cushing disease, where high-dose dexamethasone can suppress cortisol.