Although a wide variety of diagnostic tests can be used in the di-agnostic workup, three major categories of diagnostic tests are common: blood tests, urine tests, and stimulation and suppres-sion tests.
Blood tests may be used to determine hormone blood levels. For example, in a patient thought to have a thyroid disorder, serum levels of thyroid-stimulating hormone (TSH) and thy-roid hormone provide information about the nature (hypofunc-tion or hyperfunction) and site (the thyroid gland, the pituitary, or the hypothalamus) of the disorder. Other blood tests are used to detect antibodies or assess the effect of the hormone on other substances (eg, the effect of insulin on blood glucose levels). Radioimmunoassays, which are radioisotope-labeled antigentests used to measure hormones or other substances, may be performed.
Urine tests may be used to measure the amount of hormone or the end products of hormones excreted by the kidneys. One-time specimens may be obtained, or in some disorders 24-hour urine specimens are collected to measure hormones or their metabolites. For example, urinary levels of free catecholamines (norepinephrine, epinephrine, and dopamine) may be mea-sured in patients with suspected tumors of the adrenal medulla (pheochromocytoma).
Stimulation and suppression tests may be used to diagnose endocrine disorders. Stimulation tests can determine how an endocrine gland responds to the administration of stimulating hormones that are normally produced or released by the hypo-thalamus or pituitary gland. If the endocrine gland responds to this stimulation, the specific disorder may be in the hypothala-mus or pituitary. Failure of the endocrine gland to respond to this stimulation helps to identify the problem as being in the en-docrine gland itself. Suppression tests may be used to determine whether negative feedback mechanisms that normally control se-cretion of hormones from the hypothalamus or pituitary gland are intact.
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