growth hormone (somatotropin) in serum

Reference interval

• 0-5.0 ng/mL fasting sample

Principle

The Allegro HGH Immunoassay incorporates two monoclonal antibodies with high affinity & specificity for the hormone. The 2 antibodies, Ab(1) & Ab(2) are selected & prepared to be specific for distint epitopes (sites) on the hGH molecule. Both antibodies bind without competition or stearic interference from each other, & form a soluble sandwich complex:

Ab(1)__hGH__Ab(2)

One monoclonal antibody is radiolabeled for detection, [Ab(2)*], while the other monoclonal antibody is coupled to biotin [[[A17799|Biotin]]- Ab(1)]. The addition to the reaction mixture of an avidin coated plastic bead allows for a specific & efficient means of binding the sandwich complex to a solid phase via the high affinity interaction between biotin & avidin.

Avidin Coated Bead - Biotin Ab(1) - hGH - Ab(2)

Standards, controls, or patient samples are first incubated with a solution containing both the radiolabeled antibody & biotin coupled antibody. An avidin coated plastic bead is subsequently added. At the end of the incubation, the bead is washed to remove unbound components & the radioactivity bound to the solid phase is measured in a gamma counter, Since the formation of a sandwich complex occurs only in the presence of an hGH molecule, the radioactivity of the avidin bound sandwich complex is directly proportional to the amount of hGH in the sample.

A dose response curve of radioactivity vs. concentration is generated using results obtained from the standards. Concentrations of hGH present in the controls & patient sera are determined directly from this curve.

Clinical significance

The measurement of circulating hGH can be used in the assessment of hyposomatotropism & hypersomatotropism & their resultant clinical disorders.

Hyposomatotropism may be due to hypopituitarism or to an isolated defect at the hypothalamic level. Hypopituitarism may be idiopathic, or may result from such states as surgical ablation or nonsecretory pituitary tumors. Growth retardation is the most significant manifestation of hGH deficiency; but retardation may also result from the failure of adequate amounts of hGH-I (Turner's syndrome). In both of these latter situations circulating hGH levels are normal. Measurements of hGH are useful in determining whether growth retardation in children is an abnormality of secretion or physiological ineffectiveness, & also in separating those with hGH deficiency problems from those with other causes of growth failure (e.g. juvenile hypothyroidism, gonadal disorders, inadequate nutrition).

Increases

• acromegaly

Decreases

• hypopituitarism

Specimen

• The determination of hGH should be performed on serum. For best comparison with normal values, a fasting morning serum sample should be obtained. Collect blood sample in a red-top venipuncture tube & allow blood to clot. Centrifuge the sample & separate from cells.
• If the assay is performed within 24 hours after collection, the specimen should be stored in the refrigerator at 2-8 C. If the testing will be delayed more than 24 hours, the specimen should be frozen. Mix thoroughly after thawing to ensure consistency in the results. Avoid repeated freezing & thawing.
• Specimens showing particulate matter, erythrocytes, or turbidity should be centrifuged before testing.

More general terms

• growth hormone (sommatotropin) in body fluid

More specific terms

• growth hormone (somatotropin) in serum post challenge

Additional terms

• growth hormone (GH) stimulation test
• growth hormone (GH) suppression test; glucose challenge test for acromegaly
• insulin-like growth factor (IGF)-1 or somatomedin C in serum

Component of

• anterior pituitary evaluation panel

Patient information

growth hormone in serum patient information