Comprehensive Neurotransmitter Profile - 24 hr

Serotonin is synthesised from tryptophan in enterochromaffin cells of the gastrointestinal tract and in neurons of the brainstem raphe nuclei. Peripheral serotonin—comprising the vast majority of total body stores—regulates gut motility, platelet aggregation, and vascular tone. Central serotonin modulates mood, appetite, and sleep. Urinary serotonin predominantly reflects peripheral synthesis and is not a direct measure of synaptic neurotransmission in the central nervous system.

Urinary serotonin is principally used to screen for carcinoid tumours, which secrete large amounts, rather than to assess mood or psychiatric disorders. Functional-medicine interpretation of urinary serotonin as a marker of central neurotransmitter status is not validated by studies demonstrating correlation with synaptic serotonin or psychiatric symptom improvement.

Dopamine is a catecholamine synthesised from tyrosine in the adrenal medulla, sympathetic ganglia, and dopaminergic neurons. Central dopamine pathways govern motor control, motivation, reward, and executive function. Urinary dopamine originates predominantly from peripheral sympathetic and adrenal sources; it does not cross the blood–brain barrier, so urinary concentrations do not directly reflect striatal or mesocortical dopaminergic activity.

Elevated urinary dopamine is associated with phaeochromocytoma and other catecholamine-secreting tumours. Functional interpretations linking urinary dopamine to attention, motivation, or mood disorders lack robust validation; plasma and urine fractionated metanephrines are the standard for catecholamine tumours.

Norepinephrine is synthesised from dopamine in sympathetic nerve terminals and the adrenal medulla. It is the principal neurotransmitter of the sympathetic nervous system, regulating cardiovascular tone, arousal, and the stress response. Urinary norepinephrine reflects systemic sympathetic activity and adrenal output, not synaptic concentrations in the locus coeruleus or other central sites.

Urinary norepinephrine is elevated in phaeochromocytoma, paraganglioma, and states of high sympathetic drive (severe stress, pain, or hypoglycaemia). Its utility in diagnosing or managing psychiatric and mood disorders has not been validated; fractionated plasma metanephrines offer greater diagnostic sensitivity for catecholamine-secreting tumours.

Epinephrine is synthesised in the adrenal medulla from norepinephrine via phenylethanolamine N-methyltransferase. It is released in response to stress and hypoglycaemia and mediates rapid metabolic and cardiovascular adjustments. Urinary epinephrine quantifies systemic adrenal medullary secretion and does not reflect central nervous system neurotransmission.

Elevated urinary epinephrine may indicate adrenal medullary tumours or episodic stress responses. It is not a validated marker of anxiety, panic, or attention-deficit disorders; clinical assessment and guideline-based evaluations remain standard.

Gamma-aminobutyric acid is the principal inhibitory neurotransmitter in the central nervous system, synthesised from glutamate by glutamic acid decarboxylase. It does not cross the blood–brain barrier, so urinary GABA reflects peripheral synthesis in the pancreas, gut, and other tissues rather than synaptic GABA in the brain.

Urinary GABA does not serve as a validated marker of central GABAergic tone or anxiety disorders. No peer-reviewed evidence supports the use of urinary GABA to guide anxiolytic therapy or to diagnose inhibitory neurotransmitter deficits.

Glutamate is the major excitatory neurotransmitter in the central nervous system and a key intermediate in amino-acid metabolism. It does not cross the blood–brain barrier, so urinary glutamate originates from peripheral protein metabolism and does not reflect synaptic glutamate concentrations or excitotoxicity.

Urinary glutamate has not been validated as a marker of neurological excitotoxicity, seizure disorders, or mood conditions. Elevated peripheral glutamate may reflect dietary intake or metabolic turnover rather than central nervous system dysfunction.

Glycine is a non-essential amino acid that acts as an inhibitory neurotransmitter in the spinal cord and brainstem and as a co-agonist at excitatory N-methyl-D-aspartate receptors. Urinary glycine reflects whole-body amino-acid metabolism and renal handling, not synaptic glycine activity.

Urinary glycine elevation can indicate inborn errors of glycine metabolism (non-ketotic hyperglycinaemia) but does not correlate with central nervous system inhibitory tone or psychiatric symptoms. Functional interpretations are not evidence-based.

Histamine is synthesised from histidine by histidine decarboxylase and is stored in mast cells and basophils. It mediates allergic and inflammatory responses and acts as a neurotransmitter in the hypothalamus and other brain regions. Urinary histamine predominantly reflects peripheral mast-cell and gut activity, not central histaminergic neurotransmission.

Elevated urinary histamine may be seen in mastocytosis, systemic allergic reactions, or high dietary histamine intake. It is not a validated marker of central histamine pathways, sleep–wake regulation, or psychiatric disorders.

This derived ratio reflects the balance between dopamine and its metabolic product norepinephrine in the periphery. It may be influenced by the activity of dopamine beta-hydroxylase, the enzyme that converts dopamine to norepinephrine, and by adrenal versus sympathetic nerve contributions.

The DA:NE ratio is sometimes interpreted in functional medicine as a marker of enzymatic efficiency or sympathetic balance, but there is no peer-reviewed evidence linking this ratio to specific psychiatric diagnoses or treatment outcomes. It does not reflect central catecholamine metabolism.