Growth Hormone, Stimulation and Suppression Tests

Synonym/Acronym

somatotropic hormone, somatotropin, GH, hGH.

Rationale

To assess pituitary function and evaluate the amount of secreted growth hormone (GH) to assist in diagnosing diseases such as giantism and dwarfism.

Patient Preparation

The patient should fast and avoid strenuous exercise for 12 hr before specimen collection for stimulation and suppression studies. Some medications may adversely interact with the inducer used for the test, e.g., amphetamine, dextroamphetamine, and methylphenidate interact with clonidine. The requesting health-care provider (HCP) should be aware of any potential interacting medications used in the studies and advise restrictions by medical direction. Protocols may vary depending on the type of induction used.

Normal Findings

Method: Immunoenzymatic assay.

Growth Hormone

Age	Conventional Units	SI Units (Conventional Units × 1)
0–6 yr	0.1–6.2 ng/mL	0.1–6.2 mcg/L
7–17 yr
Male	0.05–11 ng/mL	0.05–11 mcg/L
Female	0.05–17.3 ng/mL	0.05–17.3 mcg/L
Adult
Male	0.05–3 ng/mL	0.05–3 mcg/L
Female	0.05–8 ng/mL	0.05–8 mcg/L
Stimulation Tests
Rise above baseline	Greater than 5 ng/mL	Greater than 5 mcg/L
Peak response	Greater than 10 ng/mL	Greater than 10 mcg/L
Suppression Tests	0–2 ng/mL	0–2 mcg/L

Other Growth Factors That May Be Requested

Insulin-like growth factor 1 (IGF1)		By Report—See Overview
Insulin-like growth factor binding protein-3 (IGFBP-3)		By Report—See Overview

Critical Findings and Potential Interventions ⬆ ⬇

Overview ⬆ ⬇

(Study type: Blood collected in a gold-, red-, or red/gray-top tube; related body system: Endocrine and musculoskeletal systems.)

GH is secreted in episodic bursts by the anterior pituitary gland; the highest level is usually secreted during deep sleep. Release of GH is modulated by three hypothalamic factors: GH-releasing hormone, GH-releasing peptide-6, and GH inhibitory hormone (also known as somatostatin). The effects of GH are carried out by insulin-like growth factors, formerly called somatomedins. GH plays an integral role in growth from birth to puberty. GH promotes skeletal growth by stimulating hepatic production of proteins; it also affects lipid and glucose metabolism. Random levels are rarely useful because secretion of GH is episodic and pulsatile.

Insulin-like growth factor 1 (IGF1) and insulin-like growth factor binding protein-3 (IGFBP-3) are growth factors involved in the regulation and promotion of growth hormone and its effects. IGF1 and IGFBP-3 are sometimes requested to assist in the identification of GH-related delays in skeletal development. IGF1 is the major biological mediator, IGFBP-3 serves as a transport protein for IFF1. Unlike GH, their circulating levels are fairly stable. Both are produced in the liver. Low levels of both are associated with either a deficiency of GH or GH resistance. Test results may vary from facility to facility. Normal range tables are lengthy as they vary by gender and age; children’s age ranges are reported for males and for females at intervals of a single year and adults (males and females) at intervals of 4 yr. The testing laboratory should be consulted for interpretation of results by report.

Stimulation tests with arginine, glucagon, insulin, or L-dopa are used to assess for deficient levels of GH production. Overproduction of GH is evaluated by performing a suppression test after administration of a glucose load, the classic screening test for acromegaly. Stimulation and suppression tests may also be used to monitor the progress of treatment.

Indications ⬆ ⬇

Assist in the diagnosis of acromegaly in adults.
Assist in establishing a diagnosis of dwarfism or growth delay in children with decreased GH levels, indicative of a pituitary cause.
Assist in establishing a diagnosis of gigantism in children with GH increased levels, indicative of a pituitary cause.
Detect suspected disorder associated with decreased GH.
Monitor response to treatment of growth delay.

Interfering Factors ⬆ ⬇

Drugs and other substances that may increase GH levels include alanine, anabolic steroids, arginine, clonidine, corticotropin, desipramine, dexamethasone, dopamine, galanin, glucagon, GH-releasing hormone, insulin, levodopa, metoclopramide, midazolam, niacin, oral contraceptives, phenytoin, propranolol, and vasopressin.
Drugs and other substances that may decrease GH levels include corticosteroids, corticotropin, hydrocortisone, and octreotide.

Potential Medical Diagnosis: Clinical Significance of Results ⬆ ⬇

Increased In

Production of GH is modulated by numerous factors, including stress, exercise, sleep, nutrition, and response to circulating levels of GH.

Acromegaly
Anorexia nervosa
Chronic kidney disease
Cirrhosis
Diabetes (unmanaged)
Ectopic GH secretion (tumors of stomach, lung)
Exercise
Gigantism (pituitary)
Hyperpituitarism
Laron dwarfism
Malnutrition
Stress

Decreased In

Adrenocortical hyperfunction (inhibits secretion of GH)
Dwarfism (pituitary) (related to GH deficiency)
Hypopituitarism (related to lack of production)

Nursing Implications ⬆

Before the Study: Planning and Implementation

Teaching the Patient What to Expect

Explain that blood samples are needed for the stimulation and suppression tests.
Discuss how this test can assist in assessing the amount of GH secreted.
Ensure that the patient is fasting and has complied with any restrictions prior to the stimulation or suppression tests.
Stimulation test using L-arginine (administered by IV) or clonidine (administered PO).
Arginine Protocol
- Explain that there may be moments of discomfort or pain experienced when the IV line is inserted for infusion of the arginine.
- Explain that specimens for either protocol (arginine or clonidine) are collected at baseline and then at 30-, 60-, 90-, and 120-min intervals after stimulation.
- Samples may be collected from the IV site if the arginine stimulation protocol is used and by venipuncture if clonadine is used. Protocols may vary between facilities.
- The patient may be asked to walk around or exercise between specimen collections in order to augment the action of the arginine.
- Explain that the arginine may cause low blood sugar; glucose monitoring may be implemented if signs and symptoms warrant, consuming a snack after the test is completed is recommended.
- Explain that clonidine lowers blood pressure, and the patient may feel dizzy or lightheaded for up to 24 hr after the test.
Stimulation test using exercise
Exercise Stimulation
- Instruct the patient to exercise vigorously for 20 min (e.g., exercising in place or running up and down stairs). A single specimen is collected immediately after the 20-min exercise period.
- Explain that specimens are collected at baseline and then at 30-, 60-, 90-, and 120-min intervals after stimulation.
Suppression test
Suppression Test Using Glucola (75 g Oral Glucose Load)
- Explain that specimens are collected at baseline and then at 30-, 60-, 90-, and 120-min intervals after suppression.

Potential Nursing Actions

Record pertinent information related to diet, sleep pattern, and activity at the time of the test.

After the Study: Implementation & Evaluation Potential Nursing Actions

Treatment Considerations

Resume usual diet, fluids, medications, and activity, as directed by the HCP.

Clinical Judgement

Consider which referrals would be the best fit to provide emotional support for body image disturbances associated with the disease process.

Follow-Up Evaluation and Desired Outcomes

Understands that additional testing may be necessary to evaluate or monitor disease progression and determine the need for a change in therapy.