Neonatal serum growth-promoting activity measured in human lymphocytes: comparison of cord and capillary blood.

The growth-promoting activity of serum was studied in 47 normal full-term newborns, comparing the effects of cord and of capillary serum upon the 3H-thymidine uptake into activated adult human lymphocytes. At birth the mean +/- SEM (TA) was significantly higher (P less than 0.001) in capillary serum (1.26 +/- 0.08 U/ml) than in cord blood (0.88 +/- 0.05 U/ml), the individual values being significantly correlated. The relatively low values in cord blood do not result from the presence of an inhibitor, nor from the cortisol levels. It may be concluded that study of cord blood is not the best means to measure growth-stimulating factors in newborns.