Test Summary

ACTH concentrations show a diurnal variation with high levels in the morning and low levels in the evening. Therefore, as with cortisol, it is important to know the collection time of the plasma sample for interpretation of the results.

Plasma ACTH measurements are useful in the differential diagnosis of Cushing's disease (ACTH hypersecretion), autonomous ACTH producing pituitary tissue (e.g. Nelson's syndrome), hypopituitarism with ACTH deficiency and ectopic ACTH syndrome. In addition to cortisol measurements, ACTH determinations can be used together with suppression or stimulation tests to diagnose the origin of glucocorticoid overproduction. Similarly, ACTH measurements can be employed to facilitate differential diagnosis of adrenocortical insufficiency (Addison’s disease).  ACTH not produced by the pituitary gland is known as ectopic ACTH; this is often associated with small cell carcinoma of the lung. In rare cases ectopic ACTH can be caused by thymic tumors, pancreatic adenocarcinomas, or bronchial carcinoids. These tumors often secrete ACTH precursors (POMC and pro-ACTH).

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