Type of test Blood

Normal findings

 Men: < 5 ng/mL (mcg/L [SI units])

Women: < 10 ng/mL (mcg/L [SI units])

 Children:

Newborn: 5-23 ng/mL (mcg/L [SI units])

1 week: 2-27 ng/mL (mcg/L [SI units])
1-12 months: 2-10 ng/mL (mcg/L [SI units])

1 year female: 0-10 ng/mL (mcg/L [SI units])

1 year male: 0-6 ng/mL (mcg/L [SI units])

Test explanation and related physiology

 This test is used to identify GH deficiency in adolescents who have short stature, delayed sexual maturity, or other growth deficiencies. It is also used to document the diagnosis of GH excess in patients with gigantism or acromegalia. GH is used to identify and follow patients with ectopic GH production by neoplasm. Finally, it is often used as a screening test for pituitary hypofunction or hyperfunction.

Because GH release is episodic, a random measurement of GH is unreliable to predict GH deficiency in adolescents. Measurement of free insulin-like growth factor (IGF) 1 and IGF BP 3 (see insulin-like growth factor, p. 544) is preferred in cases of short stature.

GH, or somatotropin, is secreted by the acidophilic cells in the anterior pituitary gland. It plays a central role in modulating growth from birth until the end of puberty. GH exerts its effects on many tissues through a group of peptides called somatomedins. The most commonly tested somatomedin is somatomedin C (also known as IGF-1), which is produced by the liver and has its major effect on cartilage.

If GH secretion is insufficient during childhood, limited growth and dwarfism may result. Also, a delay in sexual maturity may be a result in adolescents with reduced GH levels. Conversely, overproduction of GH during childhood results in gigantism, with the person sometimes reaching nearly 7 to 8 feet in height. An excess of GH during adulthood (after closure of long bone end plates) results in acromegaly, which is characterized by an increase in bone thickness and width but no increase in height.

Normal GH levels overlap significantly with deficient levels. Low GH levels may indicate deficiency or may be normal for certain individuals at certain times of the day. To negate time variables in GH testing, GH can be drawn 60 to 90 minutes after deep sleep has occurred. Levels increase during sleep. Also, strenuous exercise can be performed for 30 minutes in an effort to stimulate GH production.

To negate the common variations in GH secretion, screening for IGF-1 or somatomedin C provides a more accurate reflection of the mean plasma concentration of GH. These proteins are not affected by the time of day or food intake like GH is. A GH stimulation test (p. 479) can be performed to evaluate the body’s ability to produce GH. Growth hormone suppression testing is used to identify gigantism in children or acromegaly in the adult. If GH can be suppressed to < 2 ng/mL, neither of these condi tions exists. The most commonly used suppression test is the oral glucose tolerance test (p. 469). GH is normally suppressed when the glucose level increases. In acromegalic patients, only a slight decrease in GH occurs.

 Interfering factors

 • Random measurements of GH are not adequate determinants of GH deficiency because hormone secretion is episodic.

• GH secretion is increased by stress, exercise, and low blood glucose levels.

*  Drugs that may cause increased levels include amphetamines, arginine, dopamine, estrogens, glucagon, histamine, insulin, levodopa, methyldopa, and nicotinic acid.

* Drugs that may cause decreased levels include corticosteroids and phenothiazines.

Procedure and patient care

Before

* Explain the procedure to the patient.

 • The patient should not be emotionally or physically stressed because this can increase GH levels.

• It is preferred that the patient be fasting and well rested. Water is permitted.

 • For GH suppression testing, the patient is kept NPO after midnight.

During

 Growth hormone test G

 • Collect a venous blood sample in a red-top tube.

• Because approximately two-thirds of the total release of GH occurs during sleep, GH secretion also can be measured during hospitalization by obtaining blood samples when the patient is sleeping.

Growth hormone suppression test

• Obtain peripheral venous access with normal saline solution.

 • Obtain baseline GH and glucose levels as described previously.

• Administer the prescribed dose of glucose over 5 minutes.

 • Obtain GH and glucose levels at 10, 60, and 120 minutes after glucose ingestion.

 After

• Indicate the patient’s fasting status and the time the blood is collected on the laboratory slip. Include the patient’s recent activity (e.g., sleeping, walking, eating).

 • Send the blood to the laboratory immediately after collection.

Abnormal findings

 Increased levels

 -Gigantism

 -Acromegaly

 -Diabetes mellitus

 -Anorexia nervosa

 -Stress

 -Major surgery

 -Hypoglycemia

 -Starvation

 -Deep-sleep state

 -Exercise

Decreased levels

- Pituitary insufficiency

 -Dwarfism

 -Hyperglycemia

 -Failure to thrive

 -GH deficiency

مواضيع ذات صلة

glycosylated hemoglobin (GHb, GHB, Glycohemoglobin, Glycolated hemoglobin, Hemoglobin [Hb A1c ], Diabetic control index)

Cultivation of Streptococcus, Enterococcus, and Similar Organisms

Direct Detection Methods of Streptococcus, Enterococcus, and Similar Organisms

Immunoglobulins

Complement

Ceruloplasmin

glucose tolerance test (GTT, Oral glucose tolerance test [OGTT])

glucose, postprandial (2-Hour postprandial glucose [2-Hour PPG], 1-Hour glucose screen)

α1-antitrypsin

Albumin

Diagnostic Laboratory Tests for Mycobacterium Tuberculosis

Glucose, blood (Blood sugar, Fasting blood sugar [FBS])