Differences in somatomedin-C between short-normal subjects and those of normal height

We evaluated basal somatomedin-C (SmC) levels in 98 subjects 2 to 16.6 years of age, with height less than 3rd centile (Tanner), and in 274 healthy controls 2 to 15.8 years, with height greater than 10th centile. Growth-retarded subjects were defined as short-normal when they had normal GH release (greater than 8 ng/ml) in at least one of three tests: arginine, L-dopa, and sleep. In control subjects, there was a significant positive correlation between SmC levels and chronologic age, bone age, and pubertal stage (pubic hair, breast or testicular volume). The same correlations were present in short-normal subjects, but SmC levels were significantly lower than in normal children. The percentage of subjects with very low SmC values (less than or equal to 0.25 IU/ml in those older than 6 years, and less than 0.1 IU/ml in those younger than 6 years) was higher in the short-normal group of children older than 6 years. In growth-retarded subjects, SmC values were significantly higher (P less than 0.005) in subjects with normal GH response in at least one of the two pharmacologic tests, compared with those with normal GH response only during sleep. We conclude that short-normal subjects have, on average, low SmC values, which might indicate insufficient GH release. Therefore, current criteria to define GH deficiency and children needing treatment may be too restrictive.