[Platelet serotonin concentration in children under 5 years of age].

High platelet serotonin concentrations have been reported in children with early infantile autism. However, as yet there are no reference values regarding platelet serotonin in normal infants and young children so that it remains difficult to define the exact significance of this finding. We report here with the platelet serotonin concentration found in 57 infants and children (20 girls, 37 boys) ranging in age from 10 days to 5 years old. Our results show that mean platelet serotonin concentrations in infants and young children are significantly greater than mean values obtained in older children (+11%) and neonates in the umbilical cord (+64%). No significant variations were found relating to sex, leucocyte count and platelet count. There therefore appears to be a physiological elevation of platelet serotonin concentration in infants and young children, and this has to be taken into consideration in the interpretation of the elevated values found in cases of infantile autism.