Function tests

• Suspicion of primary (M. Addison) or secondary adrenocortical insufficiency
• Differential diagnosis of Cushing syndrome

Known hypersensitivity towards ACTH

Determination of the stim lability of the adrenal cortex by intravenous application of ACTH.

Cortisol

2 - 5 ml whole blood without supplements, before (0 min), and 30 and 60 min after ACTH administration. Centrifuge blood after 30 - 40 min and send serum to the laboratory.

Test start 7 - 9 o’clock. The patient should remain empty-stomached throughout the test.

1. Initial basal blood extraction prior to ACTH (0 min)
2. Intravenous application of 1 ampule Synacthen® (250 µg = 25 IE ACTH) as a bolus
3. Blood extractions after 30 and after 60 min. Mark samples with extraction timings.

Normal function of the adrenal cortex:

Basal cortisol values (0 min) or stimulated cortisol values (after 30 and 60 min) of ≥ 18 µg/dl – 20 µg/dl largely rule out adrenocortical insufficiency. Basal cortisol values (0 min) or stimulated cortisol values (after 30 and 60 min) of ≥ 20 µg/dl reliably exclude adrenocortical insufficiency. However the high-dose  ACTH test (250 µg Synacthen) can lead to false-negative results due to the supraphysiological stimulus, especially in case of inhalative glucocorticoid-induced (partial) adrenocortical insufficiency. In case of this question, the low-dose ACTH test with only 1 µg Synacthen should rather be used. Here, the cortisol value should be ≥ 18 µg/dl, to rule out adrenocortical insufficiency.

A secondary (hypophyseal) adrenocortical insufficiency can only be determined with the AHTH test, if atrophic adrenocortical tissue is already present. If inconclusive values are seen for basal ACTH, which is rather normal to low normal in case of adrenocortical insufficiency, a CRH test should be carried out (see there) in case of doubt.