Diagnosis of Hypopituitarism
Hypopituitarism Diagnosis: Book Excerpts
Diagnostic Tests for Hypopituitarism: Online Medical Books
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Diabetes insipidus:
Diagnosis
(Professional Guide to Diseases (Eighth Edition))
Urinalysis reveals almost colorless urine of low osmolality (50 to 200 mOsm/kg, less than that of plasma) and low specific gravity (less than 1.005).
CONFIRMING DIAGNOSIS Diagnosis requires evidence of vasopressin deficiency, resulting in the kidneys’ inability to concentrate urine during a water deprivation test.
In this test, after baseline vital signs, weight, and urine and plasma osmolalities are obtained, the patient is deprived of fluids and observed to make sure he doesn’t drink anything surreptitiously. Hourly measurements then record the total volume of urine output, body weight, urine osmolality or specific gravity, and plasma osmolality. Throughout the test, blood pressure and pulse rate must be monitored for signs of orthostatic hypotension. Fluid deprivation continues until the patient loses 3% of his body weight (indicating severe dehydration). When urine osmolality stops increasing in three consecutive hourly specimens, patients receive 5 units of aqueous vasopressin subcutaneously (S.C.).
Hourly measurements of urine volume and specific gravity continue after S.C. injection of aqueous vasopressin. Patients with pituitary diabetes insipidus respond to exogenous vasopressin with decreased urine output and increased specific gravity. Patients with nephrogenic diabetes insipidus show no response to vasopressin.
» READ BOOK EXCERPT ONLINE »
Source: Professional Guide to Diseases (Eighth Edition), 2005
Hypopituitarism:
Diagnosis
(Professional Guide to Diseases (Eighth Edition))
In suspected hypopituitarism, evaluation must confirm hormonal deficiency due to impairment or destruction of the anterior pituitary gland and rule out disease of the target organs (adrenals, gonads, and thyroid) or the hypothalamus. Low serum levels of thyroxine (T4), for example, indicate diminished thyroid gland function, but further tests are necessary to identify the source of this dysfunction as the thyroid, pituitary, or hypothalamus.
Serum insulin–like growth factor 1 (IGF-1) is decreased. Cranial computed tomography (CT) scan or magnetic resonance imaging (MRI) may reveal a tumor or abnormal mass in the pituitary gland of the hypothalamus. Radioimmunoassay showing decreased plasma levels of some or all pituitary hormones, accompanied by end-organ hypofunction, suggests pituitary failure, and eliminates target gland disease. Failure of thyrotropin-releasing hormone administration to increase TSH or prolactin concentrations rules out hypothalamic dysfunction as the cause of hormonal deficiency.
Provocative tests are helpful in pinpointing the source of low cortisol levels. Oral metyrapone blocks cortisol synthesis, which should stimulate pituitary secretion of corticotropin and the adrenal precursors of cortisol, measured in urine as hydroxycorticosteroids. Insulin-induced hypoglycemia also stimulates corticotropin secretion. Persistently low levels of corticotropin indicate pituitary or hypothalamic failure. These tests require careful medical supervision because they may precipitate an adrenal crisis.
CONFIRMING DIAGNOSIS Diagnosis of hypopituitarism requires measurement of GH levels in the blood after administration of regular insulin (inducing hypoglycemia) or levodopa (causing hypotension). These drugs should provoke increased secretion of GH. Persistently low GH levels, despite provocative testing, confirm GH deficiency. CT scan, MRI, or cerebral angiography confirms the presence of intrasellar or extrasellar tumors.
» READ BOOK EXCERPT ONLINE »
Source: Professional Guide to Diseases (Eighth Edition), 2005
Diabetes insipidus:
Diagnosis
(Handbook of Diseases)
Urinalysis reveals almost colorless urine of low osmolality (50 to 200 mOsm/kg, less than that of plasma) and low specific gravity (less than 1.005). However, a diagnosis requires the water deprivation test to provide evidence of vasopressin deficiency, resulting in the kidneys’inability to concentrate urine.
Water deprivation test
In this test, after baseline vital signs, weight, and urine and plasma osmolalities are obtained, the patient is deprived of fluids and observed to make sure he doesn’t drink anything surreptitiously. Hourly measurements then record the total volume of urine output, body weight, urine osmolality or specific gravity, and plasma osmolality. Throughout the test, blood pressure and pulse rate must be monitored for signs of orthostatic hypotension.
Fluid deprivation continues until the patient loses 3% of his body weight (indicating severe dehydration). When urine osmolality stops increasing in three consecutive hourly specimens, the patient receives 5 units of aqueous vasopressin subcutaneously (S.C.).
Hourly measurements of urine volume and specific gravity continue after S.C. injection of aqueous vasopressin. Patients with pituitary diabetes insipidus respond to exogenous vasopressin with decreased urine output and increased specific gravity. Patients with nephrogenic diabetes insipidus show no response to vasopressin.
» READ BOOK EXCERPT ONLINE »
Source: Handbook of Diseases, 2003
Hypopituitarism:
Diagnosis
(Handbook of Diseases)
In suspected hypopituitarism, evaluation must confirm hormonal deficiency due to impairment or destruction of the anterior pituitary gland and rule out disease of the target organs (adrenals, gonads, and thyroid) or the hypothalamus. Low serum levels of thyroxine (T4), for example, indicate diminished thyroid gland function, but further tests are necessary to identify the source of this dysfunction as the thyroid, pituitary, or hypothalamus.
Radioimmunoassay showing decreased plasma levels of some or all pituitary hormones, accompanied by end-organ hypofunction, including low levels of T4, estrogen, and testosterone, suggests pituitary failure and eliminates target gland disease. Failure of thyrotropin-releasing hormone administration to increase TSH or prolactin concentrations rules out hypothalamic dysfunction as the cause of hormonal deficiency.
Provocative tests are helpful in pinpointing the source of low cortisol levels. Oral metyrapone blocks cortisol synthesis, which should stimulate pituitary secretion of corticotropin and the adrenal precursors of cortisol, measured in urine as hydroxycorticosteroids. Insulin-induced hypoglycemia also stimulates corticotropin secretion. Persistently low levels of corticotropin indicate pituitary or hypothalamic failure. These tests require careful medical supervision because they may precipitate an adrenal crisis.
Diagnosis of hypopituitarism requires measurement of hGH levels in the blood after administration of regular insulin (inducing hypoglycemia) or levodopa. These drugs should provoke increased secretion of hGH. Persistently low hGH levels, despite provocative testing, confirm hGH deficiency. Computed tomography scan, magnetic resonance imaging, or cerebral angiography confirms the presence of intrasellar or extrasellar tumors.
» READ BOOK EXCERPT ONLINE »
Source: Handbook of Diseases, 2003
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