Confidently Test for Growth Disorders
Growth hormone, IGF-I, and IGFBP-3 assays for timely and accurate diagnosis of growth disorders
Growth hormone and binding proteins
GH is secreted from the pituitary gland, part of the endocrine system. Too much growth hormone (hypersecretion) can cause abnormal growth patterns called acromegaly in adults and gigantism in children. Too little growth hormone (hyposecretion) can cause a slow or flat rate of growth in children, and changes in muscle mass, cholesterol levels, and bone strength in adults.2 Clinical disorders of hyposecretion include dwarfism and unattained growth potential.3
GH works through a growth factor called IGF-1.6 A normal plasma or serum IGF-I concentration is strong evidence against GH deficiency. A low IGF-I value implies GH deficiency and requires additional testing to determine whether GH secretion is subnormal. Measurement of IGF-I is also useful in assessing change of nutritional status.3
IGFBP-3 is the main carrier of IGF-I in the body. Blood levels of both these proteins are controlled by GH. IGFBP-3 also helps extend the life of GH in the blood and helps control its effects on body tissues. Levels of IGFBP-3 are highest during childhood and puberty, and then decrease during adulthood. Levels may also be affected by sexual maturation and nutritional status.4
Growth disorders, although not common, affect thousands of people each year.
A person may be diagnosed as a child or as an adult. There are different types of growth disorders, many caused by imbalances in different types of hormones.
Growth Hormone Deficiency (GHD)
About one in 4,000 to 10,000 children have growth hormone deficiency. Some children are born with GHD (congenital), while others develop it after birth (acquired). Most children with childhood-onset GHD have no additional hormone deficiencies, and the cause is unknown.6
Excessive action of IGF-I while epiphyseal growth plates are open causes gigantism, which occurs very rarely.8 Children and adolescents with gigantism stand >2 standard deviations above the mean height for their gender and age.
Caused by hypersecretion of IGF-1, acromegaly is the most common disorder of GH excess.8 In contrast to gigantism, it occurs in adolescence and adults after their epiphyseal growth plates have fused.
The name acromegaly comes from the Greek words for “extremities” (acro) and “great” (megaly), because one of the most common symptoms of this condition is abnormal growth of the hands and feet. The symptoms of acromegaly can vary and develop gradually over time; therefore, a diagnosis of this condition may be difficult.
Early detection is a goal in the management of acromegaly because the pathologic effects of increased GH production are progressive.9 IGF-I is a reliable marker of disease activity and GH status in acromegaly.10
Results from GH, IGF-I, and IGFBP-3 tests are essential when diagnosing and treating growth disorders.
A GH stimulation or a GH suppression test is used to diagnose growth hormone disorders; a stimulation test will check for a GH deficiency, whereas a suppression test will check for a GH excess.
In the diagnosis of growth disorders, measurements of IGF-I are a useful indicator of growth hormone secretion. An IGF-I test is often ordered along with GH. IGF-I mirrors GH excesses and deficiencies, but its level is stable throughout the day, making it a useful indicator of average GH levels.11
IGFBP-3 is GH-dependent and therefore useful in the evaluation of GH secretion.
The IMMULITE® 2000/XPi GH assay is specific and sensitive and requires only a small volume of sample. The IMMULITE 2000/XPi IGF-I and IGFBP-3 assays have established age- and gender-based reference intervals that are crucial in assessing the patient’s growth condition. The IMMULITE 2000/XPi IGF-I assay is standardized to the first WHO International Standard 02/254 for IGF-I with newly established detection limits (LoD and LoQ), ensuring confidence in your laboratory’s test results.