Brief report: Platelet-poor plasma serotonin in autism.

Scientists drew blood from kids with autism and kids without. They spun the samples to remove platelets. Then they measured serotonin in the leftover plasma.

Both groups gave blood the same way. The lab used standard tools to count serotonin. Age and sex were matched so the groups were fair.

Plasma serotonin levels were the same in both groups. Kids with autism did not have extra free serotonin floating in their blood.

The old idea of 'hyperserotonemia' in autism is not coming from the liquid part of blood. The problem lives inside the platelets, not in the open plasma.

Nicholson et al. (2017) also found no signal when they checked neonatal heel-stick blood for thyroid hormones. Both studies show that single blood spots taken early in life do not predict later autism.

Bicer et al. (2013) and Moorthy et al. (2022) used the same case-control shape to look at body issues outside the brain—weight and cavities. Like the serotonin paper, they found only small or no group differences, reminding us that big biological red flags are rare.

Together these papers push clinicians to look past simple blood tests and focus on behavior and learning.

You can stop chasing plasma serotonin as a quick autism screen. Save your budget for skills assessments and parent coaching. If a pediatrician orders a 'serotonin test,' share this paper and explain that platelet handling, not blood levels, is the real puzzle.