Serum and urine somatomedin B in pediatrics

Somatomedin B was determined by the radioimmunological method in the serum and urine of 104 normal subjects divided into seven age groups. The serum and urine of each patient were divided into two fractions of which one was heated at 60 degrees C for 30 min. SmB serum levels were significantly higher in heated than in unheated samples in all age groups. Moreover, SmB levels in unheated samples increased slowly, but significantly, up to the age of four years, then decreased until nine years of age, when they started increasing again. In heated serum, however, a rapid and significant increase occurred from the age of six months; later SmB levels showed slight, not significant variations. In urine no significant difference was shown in SmB levels either between unheated and heated samples or between age groups. The difference in the behavior of SmB in serum and urine may be explained by assuming the presence of carrier proteins in the blood.