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ACTH will be low [13] – usually below 35, but most people with secondary fall within the range limit. This is inappropriately normal for the low cortisol level. In some cases, the actual cause of low ACTH is from low CRH in the hypothalamus. It is possible to have separate ACTH and CRH impairment such as can happen in a head injury. [18]
Both random total cortisol levels, total cortisol levels or increment after ACTH stimulation tests, free cortisol levels, or a combination of these have been proposed as diagnostic tests. Other stimulation tests for adrenal insufficiency which are used in non-critical patients, such as the test using metyrapone or a test which employs insulin ...
Cortisol levels typically peak in the morning; thus, low values indicate true adrenal insufficiency. [2] Urinary free cortisol can also be measured, but are not necessary for diagnosis. [2] To determine the origin of dysfunction, the ACTH stimulation test is the best initial test as it can differentiate between primary and secondary adrenal ...
Low blood sugar and hyponatremia are possible; however, blood potassium levels typically remain normal because affected patients are deficient in glucocorticoids rather than mineralocorticoids because of their intact renin-angiotensin-aldosterone system. ACTH may be undetectable in blood tests, and cortisol is abnormally low. [1]
In suspected cases of Addison's disease, demonstration of low adrenal hormone levels even after appropriate stimulation (called the ACTH stimulation test or synacthen test) with synthetic pituitary ACTH hormone tetracosactide is needed for the diagnosis. Two tests are performed, the short and the long test.
A cortisol level above 500 after achieving a low blood sugar rules out ACTH deficiency, while lower levels confirm the diagnosis. A similar stimulation test using corticotropin-releasing hormone (CRH) is not sensitive enough for the purposes of the investigation.
Low-dose and high-dose variations of the test exist. [4] The test is given at low (usually 1–2 mg) and high (8 mg) doses of dexamethasone, and the levels of cortisol are measured to obtain the results. [5] A low dose of dexamethasone suppresses cortisol in individuals with no pathology in endogenous cortisol production.
The activity of 11β-hydroxylase can be determined by observing the basal 11-deoxycortisol level. A level over 10 ng/mL, indicates followup with ACTH stimulation test. The 60th minute post-stimulation 11-deoxycortisol levels higher than 18 ng/mL are diagnostic of LOCAH. [45]