Lab Values: 137 Values You Must Know to Easily Pass the NCLEX! (Nursing Review and RN Content Guide, Registered Nurse Practitioner, Laboratory Medicine Textbooks) by Chase Hassen

Author:Chase Hassen [Hassen, Chase]
Language: eng
Format: azw3
Publisher: UNKNOWN
Published: 2015-06-16T16:00:00+00:00

Chapter 7: Endocrine Test s

The endocrine system involves a wide range of hormones sent from many glands throughout the body. Laboratory testing can help determine if a particular gland is overworking or underworking. Many hormone systems have a feedback loop that must be intact in order to have the hormone levels remain normal.

CRH and ACTH

The hypothalamus in the brain produces and releases corticotropin-releasing hormone (CRH) which triggers the pituitary gland to release ACTH, also called adrenocorticotropic hormone. This, in turn, triggers the release of cortisol from the adrenal glands, raising glucose and blood pressure while suppressing the immune system. As cortisol levels go up, ACTH levels fall. Cortisol peaks in the morning and is at a trough level by evening. Therefore, it is important to determine the time when the cortisol level is to be taken from the patient’s veins. Peak levels are done between 6 am and 8 am, while trough levels are done between 6 pm and 11 pm. It is necessary to put the blood on ice as soon as it is gotten from the patient and the test must be done as soon as possible. Things like lithium, insulin and amphetamines may increase the cortisol levels.

The normal range for ACTH at 6 am to 8 am is less than 80 pg/ml. The normal level for ACTH at 6 pm to 11 pm is less than 50 pg/ml. The normal peak ranges for cortisol are 5-23 mcg/dL and the normal trough ranges are 3-13 mcg/dL .

Elevated cortisol levels are found in physical or emotional distress, Cushing’s disease, Adrenal gland tumor, pituitary gland tumor. Low levels of cortisol can be seen in a stroke, head injury, pituitary gland tumor, adrenal gland tumor or pituitary radiation.

Comparisons are made between the ACTH and cortisol levels. For example, if the ACTH and cortisol levels are both high, then ACTH is being made outside the pituitary gland. If there are low levels of ACTH and high levels of cortisol, this can be caused by Cushing syndrome. High ACTH and low cortisol levels are found in Addison’s disease. Low levels of both ACTH and cortisol are found in situations of hypopituitarism.

Dexamethasone Suppression Test

This is a test for Cushing’s syndrome. Dexamethasone mimics cortisol in the blood and is given at 11 pm the night before the cortisol level is taken (at about 8 am). Some people metabolize dexamethasone quickly so that increased amounts of dexamethasone must be given if Cushing’s disease is suspected but the results were suboptimal. Ideally, the cortisol level should be very low after receiving dexamethasone and, if it is not, there may be an adrenal gland tumor secreting cortisol in spite of low ACTH levels. The patient may receive up to 8 separate doses of dexamethasone over a two day period of time. In a normal dexamethasone suppression test, the cortisol level will be less than 5 mcg/dL. High levels can also be seen in uncontrolled diabetes, elevated thyroid syndromes, heart attacks, heart failure, poor diet, alcoholism, depression, anorexia, fever, or lung cancer .

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