Growth Assays

Growth hormone (GH) is secreted from the pituitary gland. Measurement of GH is primarily of interest in the diagnosis and treatment of various forms of inappropriate growth hormone secretion.

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

In the diagnosis of growth disorders, measurements of IGF-I are a useful indicator of growth hormone secretion. 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
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.¹

IGFBP-3 is used as an aid in the evaluation of growth disorders. It is growth hormone (GH) dependent and therefore useful in the evaluation of GH secretion. 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 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.⁵

Growth hormone deficiency means the pituitary gland does not make enough growth hormone. Most of the time, the cause of growth hormone deficiency is unknown. It may be present at birth or develop as a result of an injury or medical condition. Severe brain injury may also cause growth hormone deficiency. Slow growth may first be noticed in infancy and continue through childhood. Although uncommon, growth hormone deficiency may also be diagnosed in adults. Possible causes include tumors involving the pituitary gland or hypothalamus, or brain radiation treatments for cancer.⁶

Gigantism–Excessive action of IGF-I while epiphyseal growth plates are open causes gigantism, which occurs very rarely⁷. Children and adolescents with gigantism stand > 2 standard deviations above the mean height for their gender and age.

Acromegaly–Also caused by hypersecretion of IGF-I, acromegaly is the most common disorder of GH excess⁸. 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 growth hormone (GH) production are progressive.⁹ IGF-I provides the most sensitive lab test for the diagnosis of acromegaly.¹⁰