Parents often become concerned when their child’s growth appears significantly different from their peers. While many factors influence a child’s height, a doctor may recommend a growth hormone stimulation test. This test helps determine if a child’s body produces adequate growth hormone, a substance important for development.
Understanding the Growth Hormone Stimulation Test
A growth hormone stimulation test evaluates the pituitary gland’s capacity to release growth hormone. It is considered when a child shows signs of growth concerns, such as being significantly shorter than average for their age and sex, or exhibiting a slow growth rate. The objective is to assess the pituitary gland’s potential, rather than simply measuring a single, random growth hormone level, which can fluctuate throughout the day.
The procedure involves administering a substance that prompts the pituitary gland to release growth hormone. Common stimulating agents include arginine, clonidine, or glucagon. Blood samples are collected at specific intervals over several hours to measure growth hormone levels. This series of measurements provides a more comprehensive picture of the gland’s function than a single blood draw.
Interpreting the Test Results
Interpreting growth hormone stimulation test results involves analyzing the peak growth hormone levels achieved after the stimulating medicine is given. A “normal” response indicates the pituitary gland is capable of producing sufficient growth hormone. While exact thresholds can vary between laboratories, a peak growth hormone level of at least 7 to 10 ng/mL is considered a normal response in children. Some experts suggest a peak above 8 ng/mL as normal, with values between 5 and 8 ng/mL considered equivocal.
Conversely, “low” or “deficient” growth hormone levels are indicated when the peak response falls below these thresholds, such as under 5 ng/mL. A subnormal result suggests a reduced amount of growth hormone stored in the anterior pituitary gland. A single test result may not always be definitive; sometimes repeat testing or additional evaluations, like a brain MRI, are necessary to confirm a diagnosis.
The results are considered in conjunction with other clinical findings, including the child’s growth patterns, bone age, and other hormone levels like insulin-like growth factor 1 (IGF-1). IGF-1 levels are useful because they remain stable throughout the day and reflect the overall effect of growth hormone. This comprehensive approach ensures an accurate diagnosis and appropriate next steps.
Underlying Causes of Low Growth Hormone
Low growth hormone levels can stem from various medical reasons. Often, the cause is unknown, termed idiopathic growth hormone deficiency. Some cases are linked to damage or abnormalities of the pituitary gland or hypothalamus, brain regions that regulate hormone production. This damage can be present from birth (congenital) or acquired later in life.
Genetic conditions can also contribute to growth hormone deficiency, sometimes involving mutations in genes important for pituitary gland development or growth hormone pathway receptors. Acquired causes may include brain tumors in the pituitary or hypothalamus, head trauma, or radiation therapy to the head, which can impact the function of these glands. Identifying the specific underlying cause helps determine the appropriate management plan for the child.
Management and Next Steps
Following a diagnosis of growth hormone deficiency, management involves growth hormone therapy. This treatment replaces the missing hormone with a man-made version, administered as daily injections under the skin. The aim of this therapy is to help the child achieve a more typical growth curve and reach an adult height within a normal range, considering their genetic potential.
The dosage of growth hormone is calculated based on the child’s weight and adjusted over time as they grow. Regular monitoring by a pediatric endocrinologist is necessary to track the child’s growth, adjust the hormone dose, and monitor for any potential side effects. Treatment continues until the child’s growth plates close or they reach their full adult height. Continued monitoring, sometimes into adulthood, can be recommended to protect various body systems.