The human growth hormone does just what you might expect: stimulates growth in humans. Secreted by the pituitary gland, the hormone is needed for growth. Irregularities cause children to grow too little or too much. In rarer cases, adults may experience abnormally high levels of HGH, which may cause the bones of the hands, feet, face and jaw to grow larger than normal. Abnormal levels may be caused by a tumor on the pituitary gland, called a pituitary adenoma. 

The growth hormone has been approved to treat patients with AIDs and HIV to counteract muscle wasting. This use led to further studies and uses for the hormone. 

HGH is now used as an anti-aging treatment. In mid-life, the pituitary gland slows production of the hormone that regulates metabolism and helps maintain organs and tissues through the growing phase and after. HGH replacement therapy is controversial, but arguably provides such benefits as an increased metabolism, increased muscle mass and decreased fat. Some adults may also experience increased bone density and a greater capacity for exercise.

The HGH blood test measures levels of the hormone in the blood. This information can be used in conjunction with additional medical testing to help diagnose a problem as well as to facilitate a discuss with a health care provider regarding the desire for HGH replacement therapy.