Whole blood serotonin and tryptophan in autism: Temporal stability and the effects of medication

Whole blood serotonin (5-HT) was significantly increased in a drug-free autistic group (n=17) compared to age-and sex-matched normal control (n =20). Blood tryptophan (TRP) values and platelet counts were similar in unmedicated autistics and normal subjects; but whole blood concentrations of TRP were significantly lower, and 5-HT values tended to be lower in the medicated group compared to unmedicated autistics. Highly significant intraclass correlation coefficients and low mean percentage differences were found for repeated measures over a year's period of whole blood 5-HT and the platelet count in the unmedicated but not in the medicated group. Blood TRP values were highly variable over time in both the medicated and drug-free autistic group