Version July 2025
GH: growth hormone; IGF-1: insulin-like growth factor 1; SD: standard deviation; rhGH: recombinant human growth hormone.
* For most patients, we use standard rhGH (somatropin), using a starting dose of approximately 35 micrograms/kg/day (for a total weekly dose of 0.24 mg/kg). For patients with severe GH deficiency, we use a lower starting dose of approximately 20 micrograms/kg/day because these individuals are more sensitive to the drug. For dosing of one of the long-acting rhGH formulations (lonapegsomatropin, somapacitan, or somatrogon), refer to local product information or UpToDate content.
¶ If rhGH is administered daily, then random sampling is sufficient for determining IGF-1 concentration. If a long-acting rhGH preparation is used, interpretation of the IGF-1 result depends on the timing of the sample compared with the preceding dose and the particular long-acting preparation because pharmacokinetics vary among these preparations; refer to UpToDate content.
Δ For monitoring rhGH therapy, target range for IGF-1 is the upper one-half of the normal range (ie, IGF-1 0 to +2 SD). IGF-1 levels below this target range are associated with subnormal growth response to therapy; IGF-1 levels above this target range (ie, >+2 SD) may be associated with possible adverse effects of rhGH. For the long-acting preparations, optimal IGF-1 targets have not been established, but it is reasonable to target mean IGF-1 values in the upper one-half of the normal range, similar to the strategy for standard rhGH preparations.
◊ If the rhGH dose is increased to >0.3 mg/kg/week but IGF-1 levels remain low (<–1 SD) despite good adherence to therapy, the patient may have GH insensitivity. If such patients also fail to have an appropriate growth response to rhGH therapy, the possibility of a GH insensitivity syndrome should be explored; refer to UpToDate content on GH insensitivity.
§ The growth response is typically considered adequate if the height velocity increases to above the 75th percentile for the child's age and gender during the period of "catch-up" growth. Refer to UpToDate topic text for details.
¥ In patients with a comorbid disease that contributes to or causes the short stature, IGF-1 levels vary depending on the nutritional status but are typically below the normal range or in the low end of the normal range.