Human growth hormone testing can be used to determine the presence of disorders of anterior pituitary hormone secretion. Serum concentrations of growth hormone are indicative of episodic or paroxysmal changes in growth hormone secretion over a 24-hour period, as well as significant physiologic changes and sleep-related changes in growth hormone secretion. Environmental and metabolic factors including nutritional intake, exercise, physical stress and exercise, and age all have an impact on the secretion and clearance of growth hormone and thus its concentration in serum. Due to the low level and rhythmic secretion of growth hormone, provocation tests are most commonly used to assess growth hormone deficiency. Abnormal growth hormone levels should be treated promptly.