Addison's disease: diagnosis
In its early stages, adrenal insufficiency can be difficult to diagnose. A review of a patient's medical history based on the symptoms, especially the dark tanning of the skin, will lead a doctor to suspect Addison's disease.
A diagnosis of Addison's disease is made by biochemical laboratory tests. The aim of these tests is first to determine whether there are insufficient levels of cortisol and then to establish the cause. X-ray examinations of the adrenal and pituitary glands also are useful in helping to establish the cause.
ACTH stimulation test
This is the most specific test for diagnosing Addison's disease. In this test, blood and/or urine cortisol levels are measured before and after a synthetic form of adrenocorticotrophic hormone (ACTH) is given by injection.
In the so-called short, or rapid, ACTH test, cortisol measurement in blood is repeated 30 to 60 minutes after an intravenous ACTH injection. The normal response after an injection of ACTH is a rise in blood and urine cortisol levels. Patients with either form of adrenal insufficiency respond poorly or do not respond at all.
When the response to the short ACTH test is abnormal, a 'long' ACTH stimulation test is required to determine the cause of adrenal insufficiency. In this test, synthetic ACTH is injected either intravenously or intramuscularly over a 48- to 72-hour period, and blood and/or urine cortisol are measured the day before and during the 2 to 3 days of the injection.
Patients with primary adrenal insufficiency do not produce cortisol during the 48- to 72-hour period; however, patients with secondary adrenal insufficiency have adequate responses to the test on the second or third day.
In patients suspected of having an Addisonian crisis, the doctor must begin treatment with injections of salt, fluids, and glucocorticoid hormones immediately. Although a reliable diagnosis is not possible while the patient is being treated, measurement of blood ACTH and cortisol during the crisis and before glucocorticoids are given is sufficient to make the diagnosis. Once the crisis is controlled and medication has been stopped, the doctor will delay further testing for up to one month to obtain an accurate diagnosis.
Insulin-induced hypoglycaemia test
A reliable test to determine how the hypothalamus and pituitary and adrenal glands respond to stress is the insulin-induced hypoglycaemia test. In this test, blood is drawn to measure the blood glucose and cortisol levels, followed by an injection of fast-acting insulin. Blood glucose and cortisol levels are measured again at 30, 45, and 90 minutes after the insulin injection. The normal response is for blood glucose levels to fall and cortisol levels to rise.
Other tests
Once a diagnosis of primary adrenal insufficiency has been made, X-ray examinations of the abdomen may be taken to see if the adrenals have any signs of calcium deposits. Calcium deposits may indicate tuberculosis. A tuberculin skin test also may be used.
If secondary adrenal insufficiency is the cause, doctors may use different imaging tools to reveal the size and shape of the pituitary gland. The most common is the CT (computed tomography) scan, which produces a series of X-ray pictures giving a cross-sectional image of a body part. The function of the pituitary and its ability to produce other hormones also are tested.
Last Reviewed: 03 June 2007
