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Growth hormone stimulation blood tests have several names such as Arginine Test, Insulin tolerance test, and Human growth hormone provocation test. They assess the capacity of the pituitary gland to release growth hormone. Because baseline levels of growth hormones are affected by many factors, growth hormone stimulation blood tests are also performed to determine responsiveness of the body to substances that normally stimulate growth hormone secretion such as Arginine and Levo-dopa. Insulin may be used to induce low blood sugar levels, which in turn stimulates growth hormone production. It has been found that blood sugar levels less than 50 mg/dL cause growth hormone levels to rise 10 times or more in normal individuals.
What are the Indications for the Test?
Growth hormone stimulation blood tests are generally ordered by physicians for individuals who have low or undetectable growth hormone levels, individuals with growth hormone deficiency, and for those who have panhypopituitarism, evidenced by having no increase after administration of a stimulant. It is also done to confirm the diagnosis of acromegaly as was indicated by reduced growth hormone output after Levo-dopa is administered as a stimulant.
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What are the Preparations prior to the Test?
The following must be done prior to the growth hormone stimulation blood test to ensure that accurate results are gathered.
- The patient should be weighed on the day of the test because dosage of the stimulant is based on the weight of the client.
- He is advised to fast from food and should avoid strenuous exercise for twelve hours before the sample is taken.
- He is also recommended to have bed rest for one and a half hours before the test is done.
- This must be strictly followed as these factors may affect the outcome of the test.
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How is the Test Done?
- Blood will be taken five times during the test procedure.
- After cleaning the puncture site in the arm vein, an intermittent venous access device is inserted at around six to eight in the morning and a blood sample is obtained. This device allows taking of the next four blood samples without puncturing the skin again.
- A 30-minute infusion of arginine is then done, followed by venous administration of a growth hormone releasing hormone (GHRH).
- At intervals of 30 minutes each, four more blood samples are taken.
- Depending on the physician, the test can be done with the arginine infusion alone or with the GHRH administration alone.
- Arginine infusion can be risky in patients with kidney or liver problems. It is often important to inform the physician about these conditions.
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What Does the Test Result Mean?
Normal values of this test are above 10 ng/mL. Indeterminate values fall between 5 to 9 ng/mL, and abnormal values are below 5 ng/mL.
Test results showing below 5 ng/mL indicate that the test did not increase the growth hormone levels in the blood. This can mean that there is a low amount of human growth hormone stored in the anterior pituitary gland. In children it is frequently associated with growth hormone deficiency in children. And in adults it is often related to panhypopituitarism.