When this occurs, ACTH levels are high which ultimately leads to increased cortisol production by the adrenal glands.

Normally, adrenal steroids then signal their presence to the brain to moderate ACTH levels (feedback inhibition).

However, in the absence of this, ACTH levels are elevated and cholesterol uptake by the cortical cells continues unabated.

If ACTH levels are too low, the adrenal glands stay in the off position.

If your doctor suspects adrenal insufficiency, he or she will check your blood cortisol and ACTH levels.

The glucocorticoids provide a reliable substitute for cortisol, thereby reducing ACTH levels.

In essence, it tests to see the source of the raised ACTH levels in a patient with Cushingoid features.

ACTH level will be low.

When cortisol levels rise, ACTH levels normally fall.

ACTH levels may be tested in the morning or evening if your doctor thinks that they are abnormal.