IGF-1 is a polypeptide of 70 amino acids (7650 daltons), and is one of a number of related insulin-like growth factors present in the circulation. The molecule shows approximately 50% sequence homology with proinsulin and has a number of biological activities similar to insulin. IGF-1 is a mediator of longitudinal growth in humans or how tall you are capable of becoming. Serum IGF-1 concentrations are altered by age, nutritional status, body composition, and growth hormone secretion. A single basal IGF-1 level is useful in the assessment of short stature in children and in nutritional support studies of acutely ill patients. For the diagnosis of acromegaly, a single IGF-1 concentration is more reliable than a random hGH measurement (Oppizi, et al., 1986). IGF-1 can be used for the assessment of disease activity in acromegaly (Barkan, et al., 198.)