Growth Hormone Suppression Test Protocol

Test Preparation and Administration

The standard protocol for growth hormone (GH) suppression testing involves administering an oral glucose load of 75g and measuring GH levels at baseline and at multiple time points afterward, with a GH nadir below 1 μg/l indicating normal suppression in adults, as recommended by the Endocrinology society 1, 2, 3
For children, the dose is weight-adjusted at 1.75 g/kg (maximum 75g) or 2.35 g/kg (maximum 100g) depending on institutional protocol, according to the Endocrinology society 1, 2

Obtain baseline GH and IGF-1 levels before glucose administration, as recommended by the Endocrinology society 1, 2, 3

In healthy adults, GH should suppress to below 1 μg/l (using standard assays) or 0.4 μg/l (using sensitive GH assays), as recommended by the Endocrinology society 1, 2, 3
GH suppression is sex and pubertal stage specific in children and adolescents, with highest levels occurring in mid-puberty (Tanner stage 2-3), particularly in girls, according to the Endocrinology society 1, 2
Approximately 30% of children with tall stature may not show GH suppression below 1 μg/l, as reported by the Endocrinology society 1, 2

Failure to suppress GH after glucose load is diagnostic of GH excess, but must be interpreted alongside clinical features and IGF-1 levels, as recommended by the Endocrinology society 1, 2, 3
IGF-1 values might be falsely normal or low in patients with GH-secreting adenoma who have concurrent severe hypothyroidism, malnutrition, or severe infection, according to the Endocrinology society 1, 2
IGF-1 may be falsely elevated in patients without GH-secreting adenoma who have poorly controlled diabetes mellitus, hepatic and/or renal failure, as reported by the Endocrinology society 1, 2
Oral estrogens can reduce IGF-1 generation by the liver, potentially confounding test results, according to the Endocrinology society 1, 2

Monitor for potential side effects if the patient is receiving GH therapy, including intracranial hypertension, glucose metabolism alterations, secondary hyperparathyroidism, and lipoatrophy at injection sites, as recommended by the medical guidelines 4
Regular clinic visits (every 3-6 months) are recommended to monitor growth parameters, pubertal development, skeletal maturation, and metabolic parameters, according to the medical guidelines 4, 5, 6, 7