Whole blood serotonin and tryptophan in autism: temporal stability and the effects of medication.
Whole-blood serotonin stays high in unmedicated autistic people—check meds before trusting lab drops.
01Research in Context
What this study did
The team drew blood from autistic people twice, one year apart. They checked whole-blood serotonin and tryptophan each time.
Some people took medicine between visits. Others did not. The study compared the two groups.
What they found
Unmedicated autistic people kept high serotonin levels all year. Their numbers barely moved.
Medication lowered both serotonin and tryptophan. The drop was big enough to change lab results.
How this fits with other research
Griffith et al. (2012) looked at plasma instead of whole blood. They found normal serotonin in autism. The two studies seem to clash, but they don't. Serotonin hides inside platelets, not plasma, so whole-blood tests catch it while plasma tests miss it.
Zhu et al. (2022) studied gut tryptophan in autistic kids. They also saw tryptophan pathway problems linked to symptom severity. This 1989 blood work and the 2022 gut work point to the same supply chain.
Heald et al. (2020) built a 34-metabolite blood panel to screen for autism risk. Their panel keeps serotonin in the mix, showing the marker still matters decades later.
Why it matters
If you order a serotonin lab, know that medication can tank the result. Note the med list and recheck after any change. Use whole-blood tests, not plasma, to spot the classic autism marker. A sudden drop may mean the client started a new prescription, not that biology shifted.
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02At a glance
03Original abstract
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 groups.
Journal of autism and developmental disorders, 1989 · doi:10.1007/BF02212724