The relationship of the A.M.
and P.M. readings are used to determine adrenal response to stress.
- Use Establish
the diagnosis of adrenocortical insufficiency, Addison's disease, adrenocortical
hypersecretion, Cushing's syndrome. Malfunction of the organs in the
hypothalamic - pituitary - adrenal cortex axis will result in alteration
of the cortisol levels. First among adrenal function tests for most
needs. Elevated levels are found in the newborn period.
Immunochemiluminometric assay (ICMA)
- Additional Information Cortisol is the
major adrenal glucocorticoid steroid hormone, and is normally under
feedback control by pituitary ACTH and the hypothalamus. Elevated values
are found in the newborn and also before death.
- Causes of low cortisol
include pituitary destruction or failure, with resultant loss of ACTH
to stimulate the adrenal, and metabolic errors or destruction of the
adrenal gland itself (adrenogenital syndromes, tuberculosis, histoplasmosis).
The diagnosis of hypoadrenalism generally requires confirmation with
ACTH stimulation, due to the circadian rhythms of cortisol and other
factors. Causes of increased cortisol, which may present initially simply
as loss of normal diurnal variation, include pituitary overproduction
of ACTH, production of ACTH by a tumor (notably oat cell cancers), and
- Dexamethasone suppression test
helps distinguish among causes of elevated cortisol.1 Dexamethasone
is a synthetic steroid which will suppress ACTH secretion. Under normal
circumstances decreased cortisol levels follow. Suppressibility of elevated
cortisol shows that feedback regulation is intact, and usually rules
out Cushing's syndrome. If there is no suppression over night after
1 mg of dexamethasone, higher doses and longer times may suppress ACTH
production by a pituitary adenoma, but will not suppress an adrenal
adenoma. Measurement of ACTH may also be informative. For the diagnosis
of adrenocortical insufficiency, the cosyntropin test is recommended.
The corticotropin-releasing hormone (CRH) stimulation test (1 g/kg bovine
CRH by I.V. administration) works well as the standard high-dose dexamethasone
suppression test in distinguishing pituitary Cushing's disease from
ectopic ACTH secretion. The test is less time consuming and can be an
outpatient test. Cortisol in ACTH response is measured at timed intervals.
A positive response (four times baseline) occurs in pituitary Cushing's
disease, and a negative response is seen in ectopic ACTH-secreting tumor.
There is a 97% positive predictive value. Cushing's is excluded in only
70% if there is nonresponse, however when both tests (dexamethasone
suppression and CRH stimulation) show no response, there is a 100% predictive
value for ectopic ACTH-secreting tumor. The stimulation test should
not be used in hypoadrenalism. For the diagnosis of Cushing's syndrome
(hypercortisolism), the urine free cortisol is the test of choice.
- The dexamethasone suppression test (DST)
is abnormal in many psychiatric illnesses. The sensitivity of the DST
in major depression is approximately 40% to 50%, but is higher (60%
to 70%) in severe (especially psychotic) affective disorders. False-positive
results occur with alcoholism and with stress (eg, hospitalization).
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