Lack of correlation between growth hormone provocative test results and subsequent growth rates during growth hormone therapy.

OBJECTIVES To determine whether there is a relationship between the peak GH level in pituitary stimulation tests and the growth rate in response to treatment with recombinant human growth hormone (GH). METHODS We identified 24 843 patients in the National Cooperative Growth Study database who had not been treated previously with GH therapy and divided them into three groups according to the peak GH level in pituitary stimulation testing: 1) <10 microg/L (n = 14 132); 2) >/=10 microg/L (n = 7476); and 3) no test results reported (n = 3235). Growth rates in each group in response to GH therapy were examined. RESULTS The children in each of the groups responded to GH therapy with a vigorous increase in growth rates (means, 8.4 to 9.5 cm/y) in the first year, followed by a gradual decline and then stabilization at 1.0 to 1.9 cm/y greater than the pretreatment values. There were large overlaps in the growth rates among the groups, but the differences were significant. The growth rates in a smaller group of children (n = 187) who had normal GH responses and normal growth rates before GH therapy increased similarly in the first year of therapy (to 7.7 to 9.2 cm/y), but then declined rapidly to the pretreatment values or lower. CONCLUSION Because the GH response to pituitary stimulation testing is inadequate for diagnosing GH deficiency, such testing also is inadequate for determining whether GH treatment should be prescribed in a child with short stature. In addition, the waning response to GH therapy in normally growing short children suggests that this treatment may not have a sustained benefit in these children.