Human Growth Hormone (hGH)

What is Growth hormone (GH)?

Growth hormone (GH) is a vital hormone crucial for normal growth and development, especially in children. It plays a pivotal role in facilitating appropriate linear bone growth from birth to puberty. In both children and adults, GH contributes to the regulation of several essential functions, including:

1. Metabolism, governing the rate at which the body converts food into energy.
2. Synthesis of lipids, proteins, and glucose (sugar).
3. Control over the production of red blood cells.
4. Maintenance of muscle mass.

What is the purpose of the test?

GH stimulation testing is requested when a child exhibits signs and symptoms of growth hormone deficiency, including:

1. Slowed growth rate during early childhood.
2. Shorter stature compared to peers of the same age, despite experiencing normal or increased weight gain.
3. Delayed onset of puberty.
4. Delays in bone development, as evident in X-ray results.

For adults, stimulation testing may be considered when there are indications of growth hormone deficiency and/or hypopituitarism, such as:

1. Reduced bone density.
2. Fatigue.
3. Adverse lipid profiles, like elevated cholesterol levels.
4. Decreased exercise tolerance.

Typically, other hormone tests, such as thyroid testing, are initially performed to rule out other conditions that might present similar symptoms. It's worth noting that GH deficiency is rare in both children and adults.

GH suppression testing, while infrequent, may be conducted when children or adults display symptoms indicative of GH excess, such as gigantism or acromegaly.

Furthermore, GH and IGF-1 testing might be scheduled at regular intervals over many years to monitor for excessive GH levels.

What does the result mean?

GH Stimulation Test:

If, during a GH stimulation test, your GH levels fail to show a significant increase (remaining lower than expected), and you exhibit signs and symptoms of growth hormone deficiency, including low IGF-1 and/or IGFBP3 levels, it's likely that you have a GH deficiency that your healthcare provider may consider treating.

In instances where your TSH and/or T4 levels are abnormal, addressing these thyroid abnormalities will likely take precedence, as thyroid disorders can produce symptoms akin to those of growth hormone deficiency. This may also indicate the presence of hypopituitarism or a more general decline in pituitary function. GH testing for GH deficiency should only be conducted after a thorough evaluation of your thyroid function. In the case of childhood hypothyroidism, treatment should be initiated, and the child's growth rate should be assessed before contemplating GH testing.

Furthermore, if rigorous exercise fails to provoke an increase in GH levels, it may suggest a GH deficiency, necessitating further follow-up testing. Children diagnosed with GH deficiency who have been receiving GH medications throughout childhood will require retesting once they have completed their growth.

GH Suppression Test:

If, during a GH suppression test, your GH levels do not significantly decrease (remaining higher than expected), and you exhibit signs and symptoms of excessive GH production, such as gigantism or acromegaly, along with elevated IGF-1 levels (if measured), it's probable that you are producing an excess of GH. In cases where imaging scans, typically MRI, reveal the presence of a mass, a pituitary tumor (usually benign) is the likely culprit.

For those under surveillance following successful tumor treatment, a resurgence in GH levels may indicate a recurrence.

What other laboratory tests might be helpful to add to the growth hormone testing?

1. Prolactin.
2. Free T4 or total T4.
3. Thyroid-stimulating hormone (TSH).
4. Cortisol.
5. Follicle-stimulating hormone (FSH).
6. Luteinizing hormone (LH).
7. Testosterone.

Typically, these tests are performed prior to GH testing to ensure that they yield normal results or are effectively managed with medication before GH assessment is initiated. For instance, it's essential to treat hypothyroidism before conducting GH deficiency testing in children to avoid potential false low GH results.

Additionally, other tests, such as insulin-like growth factor binding protein-3 (IGFBP-3), may be occasionally ordered to assist in the evaluation of GH production.