Type of test Blood

 Normal findings

GH levels > 10 ng/mL or > 10 mcg/L (SI units)

IGF-1 > 80 ng/mL

Test explanation and related physiology

Because GH (see previous test) secretion is episodic, a random measurement of plasma GH is not adequate to make a diagnosis of GH deficiency. IGF-1 screening followed by GH stimulation is indicated for children and adults suspected of GH deficiency. To diagnose GH deficiency, GH stimulation tests are sometimes needed. One of the most reliable GH stimulators is insulin-induced hypoglycemia, in which the blood glucose declines to less than 40 mg/dL. Other GH stimulants include vigorous exercise and drugs (e.g., arginine, clonidine, glucagon, levodopa). Glucagon is more widely used for GH stimulation, especially if there are safety concerns with insulin-induced hypoglycemia.

This test can also evaluate the entire hypothalamic–pituitary– adrenal endocrine pathway. Induced hypoglycemia is a potent stressor that strongly instigates ACTH and cortisol besides growth hormone.

Usually a double-stimulated test is performed using an arginine infusion followed by insulin-induced hypoglycemia. A GH con centration of more than 10 mcg/L after stimulation effectively excludes the diagnosis of GH deficiency. Hypothyroidism should be excluded before GH stimulation testing.

Contraindications

 • Patients with epilepsy

 • Patients with cerebrovascular disease

 • Patients with myocardial infarction

 • Patients with low basal plasma cortisol levels Potential complications

 • Hypoglycemia so significant and severe as to cause ketosis, acidosis, and shock; with close observation, this is unlikely

Procedure and patient care

 Before

* Explain the procedure to the patient and, if appropriate, to the parents.

* Instruct the patient to remain NPO after midnight on the morning of the test. Water is permitted.

• Ensure that a syringe of 50% glucose solution is readily available in the event of severe hypoglycemia.

During

 • Note the following procedural steps:

 1. A saline lock IV line is inserted for the administration of medications and for the withdrawal of blood samples.

 2. Baseline blood levels are obtained for GH, glucose, and cortisol.

3. Venous samples for GH are obtained at 15, 30, 45, 60, 90, and 120 minutes after injection of arginine, insulin, or glucagon. A typical dose of insulin is 0.1-0.25 u of regular insulin per kg body weight. Redosing may be required if glucose does not decrease by 30 minutes.

4. Blood glucose levels can also be monitored with a glucometer. The blood sugar should drop to less than 40 mg/dL for effective measurement of GH reserve.

• Monitor the patient for signs of hypoglycemia, postural hypo tension, somnolence, diaphoresis, and nervousness. Ice chips are often given during the test for patient comfort.

• This procedure is usually performed by a nurse with a physician in proximity.

• This test takes approximately 2 hours to perform.

* Tell the patient that the minor discomfort associated with this test results from the insertion of the IV line and the hypoglycemic response induced by the insulin injection.

• GH also can be stimulated by vigorous exercise. This entails running or stair climbing for 20 minutes. Blood samples of GH are obtained at 0, 20, and 40 minutes.

 After

• Observe the venipuncture site for bleeding.

• Send the blood to the laboratory immediately after collection.

• Give the patient cookies and punch or an IV glucose infusion.

* Inform the patient and family that results may not be available for approximately 7 days. Some laboratories run GH tests only once per week.

 Abnormal findings

- Growth hormone deficiency

- Pituitary deficiency

اخر الاخبار

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مواضيع ذات صلة

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