The first-year growth response to growth hormone treatment predicts the long-term prepubertal growth response in children

BACKGROUND Pretreatment auxological variables, such as birth size and parental heights, are important predictors of the growth response to GH treatment. For children with missing pretreatment data, published prediction models cannot be used. The objective was to construct and validate a prediction model for children with missing background data based on the observed first-year growth response to GH. The accuracy and reliability of the model should be comparable with our previously published prediction model relying on pretreatment data. The design used was mathematical curve fitting on observed growth response data from children treated with a GH dose of 33 microg/kg/d. METHODS Growth response data from 162 prepubertal children born at term were used to construct the model; the group comprised of 19% girls, 80% GH-deficient and 23% born SGA. For validation, data from 205 other children fulfilling the same inclusion and treatment criteria as the model group were used. The model was also tested on data from children born prematurely, children from other continents and children receiving a GH dose of 67 microg/kg/d. RESULTS The GH response curve was similar for all children, but with an individual amplitude. The curve SD score depends on an individual factor combining the effect of dose and growth, the 'Response Score', and time on treatment, making prediction possible when the first-year growth response is known. The prediction interval (+/- 2 SD res) was +/- 0.34 SDS for the second treatment year growth response, corresponding to +/- 1.2 cm for a 3-year-old child and +/- 1.8 cm for a 7-year-old child. For the 1-4-year prediction, the SD res was 0.13 SDS/year and for the 1-7-year prediction it was 0.57 SDS (i.e. < 0.1 SDS/year). CONCLUSION The model based on the observed first-year growth response on GH is valid worldwide for the prediction of up to 7 years of prepubertal growth in children with GHD/ISS, born AGA/SGA and born preterm/term, and can be used as an aid in medical decision making.