The goal of this observational study is to measure serotonin levels in in a control cohort.

The main question aims to determine the mean serum serotonin level in a cohort of adult controls, based on age and sex.

This will allow for the establishment of reference values. We will also measure the different metabolites of tryptophan. These measurements will be performed on residual blood samples in the laboratory, after blood collection carried out as part of routine care. Thus, patients will not need to undergo an additional blood draw.

Serotonin (5-HT or 5-hydroxytryptamine) is a monoamine primarily recognized for its role as a neurotransmitter in the central nervous system (CNS). It is synthesized from tryptophan, which is also essential for the production of metabolites in the kynurenine and indole families.

However, serotonin's functions extend beyond the CNS: various peripheral tissues have the capacity to produce and/or utilize serotonin locally, forming systems referred to as "micro-serotonergic." Among serotonin's peripheral roles, it has been demonstrated to positively influence erythropoiesis and red blood cell survival, iron metabolism, skin pigmentation, as well as placental and embryonic development during pregnancy.

In humans, there is no established standard for blood serotonin levels. It is known that, aside from major events, an individual's serotonin levels remain stable throughout life, but it is likely that blood serotonin levels depend on age and sex.

We aim to establish a cohort of adult control patients, for whom we will measure serum serotonin and the different metabolites of tryptophan, to analyze whether serotonin varies according to sex and age, and to determine its average serum levels.

Preliminary data from the laboratory suggest a role for serotonin in iron metabolism. Therefore, as a secondary objective, we also intend to perform an iron status assessment in control patients to analyze whether there are variations in iron parameters based on serotonin levels.

This cohort could also serve as a comparison point for future studies of serum serotonin levels in pathological conditions or during pregnancy.

Inclusion Criteria:

• Adult patients aged ≥ 18 years
• Who have undergone a blood draw at CHSF during the recruitment period
• With hemoglobin, white blood cell, and platelet counts within the laboratory's normal ranges
• With a C-reactive protein (CRP) level < 30 mg/L

Exclusion Criteria:

• Patients informed about the study who decline participation
• Patients with a current diagnosis or history of psychiatric disorders
• Patients on antidepressants or narcotics at the time of sampling

The study population is a control cohort. We will include adult patients aged 18 years or older who have undergone a blood draw at CHSF during the recruitment period. Eligible participants must have hemoglobin, white blood cell, and platelet counts within the laboratory's normal ranges, and a C-reactive protein (CRP) level below 30 mg/L.