Growth Hormone (GH) Test Guide

What Is Growth Hormone (GH)?

While its name suggests a role confined to childhood height, growth hormone (GH) is a busy and vital chemical messenger throughout life. Produced by the pea-sized pituitary gland at the base of your brain, GH is a key regulator of metabolism, body composition, and cellular repair. In my clinical practice, I often see adults who are surprised to learn their fatigue, muscle weakness, or unexplained weight changes can be linked to a GH imbalance, long after their height is set.

What Does Growth Hormone Do in the Body?

Think of GH as a master orchestrator, not a soloist. It works primarily by stimulating the liver to produce insulin-like growth factor 1 (IGF-1), which then carries out many of GH's effects. Its main roles include promoting protein synthesis for muscle growth, breaking down fat for energy, and regulating blood sugar levels. For children, its role in stimulating bone and cartilage growth is, of course, critical. However, in adults, it remains essential for maintaining healthy muscle mass, bone density, and cardiovascular health.

Why Is a Growth Hormone (GH) Blood Test Done?

A single, random GH blood test is rarely diagnostic on its own because GH is released in pulses, especially during sleep, stress, and exercise. Levels can vary widely throughout the day. Therefore, GH testing is almost always interpreted alongside IGF-1 levels, which provide a more stable, integrated picture of GH secretion over the preceding 24 hours.

Is High GH Dangerous? When Is Testing Ordered?

Suspicion of a GH-producing pituitary tumour is the most common reason for testing. If a tumour (adenoma) produces too much GH, the consequences depend on age. In children whose growth plates are open, it causes gigantism, resulting in excessive height. In adults, it leads to acromegaly, a condition marked by the gradual enlargement of hands, feet, and facial features. My patients typically first notice they need larger rings or shoe sizes, or that their jaw seems more prominent. Testing is crucial for diagnosis.

Suspected GH Deficiency (GHD)

In children, GHD results in poor growth and short stature. In adults, it can develop after pituitary surgery, radiation, or trauma and often causes a cluster of non-specific symptoms: increased body fat (particularly abdominal), decreased muscle mass, low energy, poor bone density, and adverse changes in cholesterol levels. Diagnosing adult GHD requires specific stimulation tests.

Growth Hormone (GH) Test Ranges

Due to its pulsatile nature, a "normal" random GH level is not definitively established and is highly context-dependent. Interpretation is complex and depends heavily on the test context (e.g., fasting, post-glucose). The table below provides a general guide for GH levels during specific diagnostic tests.

Note: Reference ranges can vary between laboratories. ng/mL = nanograms per millilitre.

The LOINC Standard for GH Testing

The internationally recognised LOINC (Logical Observation Identifiers Names and Codes) code for a Growth Hormone test in blood serum or plasma is 2047-7. This code standardises the test name as "Growth hormone (GH) [Mass/volume] in Serum or Plasma", ensuring clear communication between healthcare providers and laboratories worldwide.

Understanding Your GH Test Results

Interpreting a GH result is not a simple case of high or low. An endocrinologist will correlate it with IGF-1 levels, clinical symptoms, and often the results of dynamic function tests.

What Does a High GH Level Mean?

In the context of a concurrently high IGF-1 level and classic symptoms, a high random GH strongly points towards acromegaly (in adults) or gigantism (in children). The definitive test is the oral glucose tolerance test (OGTT), where a patient drinks a glucose solution. In healthy individuals, GH suppresses sharply. In acromegaly, it does not.

What Does a Low GH Level Mean?

A low random GH level is expected in healthy, fasting adults. A diagnosis of GH deficiency (GHD) cannot be made from a single low value. Instead, it requires a stimulation test, such as the insulin tolerance test (ITT) or arginine + GHRH test, where provocative agents are given to try and stimulate the pituitary to release GH. A failure to respond adequately confirms GHD.

GH and Pituitary Tumours

Most cases of GH excess are due to a benign pituitary adenoma. Evaluation always includes a pituitary MRI to visualise the gland. Treatment is multidisciplinary, involving endocrinologists and neurosurgeons, and may include surgery, medication (like somatostatin analogues), or radiation therapy to normalise hormone levels.

What Is the Insulin Tolerance Test for GH?

The insulin tolerance test (ITT) is the historical gold standard for diagnosing adult GH deficiency. Under careful medical supervision, insulin is administered to induce controlled hypoglycaemia (low blood sugar), which is a powerful stimulus for GH release. Blood is drawn at intervals to measure the GH response. A blunted peak confirms deficiency. Due to the risks of hypoglycaemia, this test is only performed in specialised units with close monitoring.

Managing Growth Hormone Disorders

Effective management is highly specific to the diagnosis. For acromegaly, the goal is to reduce GH and IGF-1 to normal levels, which often reverses symptoms and prevents long-term complications like heart disease, diabetes, and arthritis. For GH deficiency, treatment involves daily injections of biosynthetic human growth hormone (somatropin), which can dramatically improve body composition, energy levels, and quality of life when prescribed appropriately.