The effect of growth hormone treatment on somatomedin levels in growth hormone-deficient children.

Serum levels of immunoreactive somatomedin (IRSM) and insulin-like activity (ILAs) by receptor assay have been measured in 177 GH-deficient (GHD) children treated with 2 U GH three times weekly for 6-10 months. The overall mean (+/- SD) pretreatment IRSM and ILAs levels were 0.21 +/- 0.30 and 0.39 +/- 0.25 U/ml, respectively. Pretreatment IRSM and ILAs levels were in the normal range for chronological age and sex in 15.8% and 33% of these GHD children. Mean IRSM and ILAs levels increased after 1 month of therapy to 0.36 +/- 0.51 and 0.62 +/- 0.33 U/ml, respectively (P less than .0001). The increase in serum IRSM levels (from 0.2 to 2.0 U/ml) that normally occurs from 1-16 yr of age is also evident in untreated GHD children, albeit to a lesser extent. In addition, the mean increase in IRSM after GH was greater in older patients. However, individual responses varied greatly. An increase in IRSM or ILAs with an increase in height velocity (HV) was observed in the majority of children, but all other combinations occurred, including increased SM with decreased HV, decreased SM with increased HV, and decreased SM with decreased HV. In summary 1) age-dependent factors in GHD children importantly influence basal and treatment SM leels; 2) a basal SM level is not a very sensitive diagnostic test, since a significant proportion of GHD children have SM levels in the normal range; and, 3) SM levels in individual patients may not increase with GH therapy and, thus, cannot be used to predict a clinical response to GH therapy.