Diagnostic Tests Static Tests Dynamic Tests
{"Image DocumentName": "Diagnostic Tests Static Tests Dynamic Tests", "Image ImageDescription": "Cortisol, ACTH, Adrenal Androgens. Mineralocorticoid status. Serum electrolytes. Plasma renin activity (PRA), direct [renin] Dynamic Tests. Short ACTH stimulation test: Serum cortisol levels are measured before and 60 minutes after the rapid IV infusion of synthetic ACTH (cosyntropin) Tests of ACTH secretory ability. Insulin-induced hypoglycemia. Glucagon. Metyrapone test. CRH stimulation test: helps determine if 2o or 3o AI. PRA is a measure of the rate of conversion of angiotensinogen to angiotensin I [7], and direct renin measures the concentration of renin in the blood. Cortisol secretion is deficient in patients with primary adrenal insufficiency despite the fact that their ability to secrete ACTH is intact. Conversely, patients with secondary or tertiary adrenal insufficiency have intrinsically normal but atrophic adrenal glands that are capable of producing cortisol but fail to do so because ACTH secretion is deficient. PLASMA RENIN ACTIVITY. - Secondary adrenal insufficiency (ACTH deficiency) is diagnosed if there is a poor cortisol response to tests of ACTH secretory ability (in addition to low 8 a.m. cortisol and low ACTH). - Tertiary adrenal insufficiency (deficient secretion of CRH) is diagnosed if the tests of ACTH secretory ability are low (in addition to low 8 a.m. cortisol and low ACTH), and if ACTH levels rise in response to CRH. In the rare circumstance of a defective CRH receptor, there will be no CRH-stimulated rise in ACTH secretion. nsulin-induced hypoglycemia \u2014 This is the most sensitive standard test of ACTH release. Serial measurements of blood glucose and cortisol are made before and at 15, 30, 45, and 60 minutes after an infusion of insulin (0.05 units/kg). The peak cortisol level should be at least double the baseline level or greater than 20 mcg/dL [8]. If desired, samples for growth hormone can be obtained at the same time. A normal GH response is usually defined as \u226510 mcg/L. (See Diagnosis of growth hormone deficiency in children , section on GH stimulation tests). Symptomatic hypoglycemia is desirable during the test, but marked changes in levels of consciousness or blood glucose <30 mg/dL must be treated with prompt administration of intravenous dextrose. The test is not recommended for children younger than 3 years old because of the risk of damage to the central nervous system resulting from hypoglycemia. Glucagon stimulation test \u2014 This test is more appropriate in children younger than 3 years. After an intramuscular injection of glucagon, the blood glucose level initially rises then drops rapidly because of the release of endogenous insulin. Serum cortisol and growth hormone levels should increase in response to this fall in blood glucose [9]. Metyrapone test \u2014 This test also is used in the assessment of ACTH secretory ability, but is rarely used clinically. Metyrapone blocks the activity of the enzyme 11-beta-hydroxylase, which is needed to convert 11-deoxycortisol to cortisol, causing a decrease in serum cortisol levels (show figure 2). In a normal patient, the decrease in cortisol levels will stimulate ACTH secretion and increase the production of cortisol precursors. This can be measured by a rise in serum levels of ACTH and 11-deoxycortisol and/or in urinary 17-hydroxycorticosteroids and free cortisol. The ACTH-stimulated gland eventually overrides the enzymatic block, allowing cortisol production to occur. However, patients must be observed closely during this test because acute adrenal insufficiency may be precipitated if the patient has marked ACTH deficiency. (See Metyrapone stimulation tests )", "Image XResolution": "37", "Image YResolution": "37", "Image ResolutionUnit": "Pixels/Centimeter", "Image Software": "SlidePlayer", "Image YCbCrPositioning": "Centered"}