Dynamic Tests in Endocrinology

Dynamic tests in endocrinology are based on an understanding of key regulators of hormonal secretion. A simple rule of thumb is to suppress a hormone if you suspect it is being over-secreted. Conversely, stimulate a hormone if you suspect it is being under secreted or absent.

Visual infographics summarize the rationale, limitations, performance, and interpretation of each test. Basic physiologic concepts are highlighted, to facilitate an appreciation of each test. Each infographic can be downloaded for printing purposes (pdf version available).

This is a sample visual infographic

Cosyntropin (cortrosyn) stimulation test :  A dynamic test for the evaluation of suspected adrenal insufficiency. The test cannot distinguish between primary and secondary AI
   
Limitations of this test
Estrogen in OCPs may increase corticosteroid-binding globulin and thus increase total serum cortisol.Low albumin can lead to a spuriously low serum cortisolIt does not distinguish between primary and secondary AI (normal stimulation test if adrenocortical atrophy has not set in yet)  
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Growth hormone suppression test : This dynamic test is used for the evaluation of suspected acromegaly.

Limitations of this test
GH levels may not be suppressed in patients liver disease, renal insufficiency, uncontrolled DM, pregnancy, estrogen therapy or anorexia.Possibility of a paradoxical increase in GH during an oral glucose tolerance test.
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GHRH-Arginine Growth hormone stimulation test :  This dynamic test is used for the evaluation of suspected growth horĀ­mone deficiency. Alternatives include the ITT and Glucagon stimulation testsPrint version
Glucagon Stimulation Test:  This dynamic test is used for the evaluation of suspected growth hormone deficiency. Alternatives include the ITT and GHRH-arginine.

Limitations of this test
Associated with significant nausea and vomiting. As a precaution, patients should therefore be nil per os, except for water, after midnight and during the test. Prophylactic anti-emetics are advised.Risk of hypoglycemia after the test (consuming small meals is reasonable)
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Insulin Tolerance Test :  This dynamic test is used for the evaluation of suspected growth horĀ­mone deficiency. It is a gold standard test for evaluating suspected secondary adrenal insufficiency.  
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