Dexamethasone suppression test

from Wikipedia, the free encyclopedia

The dexamethasone suppression test ( DST or dexamethasone inhibition test ) is used in human and veterinary medicine to exclude and differentiate between the causes of Cushing's syndrome .

The test

It is a provocation test. In a healthy organism, there is a control loop between the adenohypophysis (this is part of the pituitary gland ), the adrenal cortex and the cortisol blood content. If the latter drops, the pituitary gland produces more adrenocorticotropin (ACTH), which stimulates the adrenal cortex to increase cortisol production. When the cortisol in the blood is increased, the pituitary gland reduces the production of the control hormone .

With DST, a small amount of dexamethasone (a synthetic cortisol derivative) is given orally or intravenously. This causes an inhibition of the cortisol production and leads to a suppression of the release of ACTH with prolonged application. A significant decrease (suppression) of the blood cortisol level can be demonstrated in a healthy organism, but not in the case of Cushing's syndrome.

Since the cortisol level is subject to strong diurnal fluctuations ( circadian rhythm ) and stress-related fluctuations, several blood withdrawals are required depending on the test used.

Executions

In humans

Short dexamethasone test

The short test is mainly used to rule out Cushing's syndrome. This is extremely unlikely if the cortisol levels drop.

There is a low-dose and a high-dose variant. The former is carried out with a single dose of 1–2 mg dexamethasone orally, the latter with up to 8 mg dexamethasone. The application takes place in the evening between 10 p.m. and 11 p.m.

Normally, the blood value of the cortisol must be determined on two consecutive days before and after the administration of dexamethasone. It is important that this measurement be taken at the same time of day, usually between 8 a.m. and 9 a.m.

Occasionally, a short test with a single measurement is also used. This is less informative, but can be better achieved in an outpatient setting.

Dexamethasone long test

The long test is used to differentiate the cause of Cushing's syndrome. A significantly delayed fall in cortisol would indicate a disruption of the pituitary - hypothalamic axis. In the absence of a drop in plasma levels, one would have to suspect autonomous cortisol production or ACTH production in a tumor.

The long test takes 3–4 days and is carried out with a total of 8–12 mg of dexamethasone. Both the daily measurements of the cortisol plasma level and the application of the drug should always take place at the same times: Usually the measurement in the morning and the application in the evening.

If a significant reduction in the cortisol plasma level can be measured after the first day, the test should be discontinued, as Cushing's syndrome would be unlikely.

With the animal

The DST is available as a high-dose and low-dose version, as a long or short protocol. The high-dose test can be used to differentiate between primary and secondary Cushing's syndrome in dogs ( canine Cushing's syndrome ). In primary Cushing's syndrome, a tumorous change in the adrenal cortex is suspected; in secondary Cushing's syndrome, the part of the pituitary gland that controls the adrenal cortex is tumorous. In both cases, there is an overall increased production of the hormone cortisol, combined with far-reaching effects, e.g. B. on metabolism and immune system. In horses ( equines Cushing's syndrome - ECS) and cats (feline Cushing's syndrome ), only the low-dose test is indicated, since a tumorous change in the adrenal cortex (primary Cushing's syndrome ) is extremely unlikely.

With the Long Protocol, a third blood sample is taken for a more precise assessment and the cortisol blood level is determined.

Problems and alternatives

In humans

Clarifying the cause of Cushing's syndrome is difficult and cannot be adequately answered by the DST. A positive DST does not prove Cushing's syndrome.

As additional diagnostics can

  • CRH test
  • Insulin hypoglycemia test and
  • 24-hour cortisol determination in urine

be performed. In addition, imaging methods ( X-ray , CT , MRT , scintigraphy ) can be used to search for a tumor.

With the animal

The DST is only about 80% negative-correct. If the result is negative, there is a residual risk of 20% that the animal will still have Cushing's syndrome.

If a horse suspected of having ECS ​​has laminitis , the use of dexamethasone is controversial. However, the amount of dexamethasone used in DST (about a twenty-fifth of the smallest therapeutic amount) is rather too small to trigger laminitis.

The DST is technically easier to use and cheaper than its alternative, the determination of the endogenous ACTH level. However, with DST, two blood samples must be taken at intervals in a very narrow time window, while the ACTH determination only requires a single blood sample.

literature

  • C. Auernhammer, CJ Auernhammer, D. Engelhardt, B. Göke: Practice book Endocrinology and Metabolism. Elsevier, Urban & Fischer-Verlag, 2004, ISBN 3-437-23360-2 .
  • J. Fritze: The medical assessment: legal questions, functional tests, assessments. Springer, 2008, ISBN 978-3-7985-1563-5 .

Web links

Individual evidence

  1. ↑ Klemens Marischler: Endocrinology. Elsevier-Verlag, p. 78.