5-HTP

5-HTP is the immediate precursor to serotonin. Your body makes it, and it's also sold as a supplement. This test measures 5-HTP in urine using LC-MS. A urine result reflects the compound that reaches the sample after production, conversion, and kidney handling; it doesn't directly measure how quickly your body makes serotonin.

Urinary 5-HTP remains a research-stage marker. Standardized clinical decision limits and health targets haven't been established, and testing hasn't been shown to improve decisions about mood, sleep, nutrition, or longevity. Published disease associations are useful research findings, but they don't yet provide a reliable interpretation of an individual result.

From Tryptophan to Serotonin

Tryptophan is an amino acid supplied by food. The enzyme tryptophan hydroxylase converts it into 5-HTP, helping regulate serotonin production. A second enzyme converts 5-HTP into serotonin. Serotonin is then broken down into several compounds. One major product is 5-HIAA, which leaves your body in urine.

Cells in the intestinal lining make much of the body's serotonin, while the brain makes its own supply. Serotonin in the circulation doesn't readily cross into the brain. 5-HTP can cross, but its concentration in urine hasn't been validated as a measure of brain serotonin production or availability.

Your body also breaks down tryptophan through a separate series of reactions called the kynurenine pathway. Measuring products from both routes doesn't establish how much tryptophan was diverted between them or identify the cause of a change.

Gut bacteria can transform 5-HTP too. Experiments with human stool samples showed conversion into 5-hydroxyindole, and a small human supplementation experiment found more of that compound in stool. These findings concern bacterial metabolism and stool measurements. They don't establish a way to assess your gut microbiome from urinary 5-HTP.

What a Urine Result Represents

Production and conversion both affect how much 5-HTP is available, but a urine concentration also depends on what the kidneys process and excrete. Human infusion experiments found large changes in urinary 5-HTP and serotonin without corresponding changes in blood serotonin. Those experiments used administered precursors and older analytical methods, so they don't establish an interpretation for an untreated person's result from this assay.

A low result cannot distinguish reduced production from increased conversion or differences in excretion. A high result cannot establish that conversion to serotonin is blocked. Adding 5-HIAA, tryptophan, or kynurenine-pathway measurements doesn't turn these possibilities into a validated diagnostic algorithm.

Severe Viral Infection

A study of people hospitalized with severe fever with thrombocytopenia syndrome found higher urinary 5-HTP in those who died than in survivors. Its ability to distinguish those outcomes was moderate. The nearly perfect discrimination reported elsewhere in the study concerned infected people versus healthy controls, a different comparison.

The researchers used LC-MS profiling with relative signals and urine-concentration adjustment. They weren't evaluating this specific quantitative assay. The study supports investigating tryptophan metabolism during severe illness; it doesn't establish a general infection-risk test or a predictable effect of an ordinary cold on your result.

Autism in Children

In a study of 44 autistic children and 44 neurotypical siblings, the subgroup with severe symptoms had a median urinary 5-HTP level about 44% lower than the control group. The difference between the entire autism group and controls wasn't statistically clear.

This was a small study using a research urine assay. It doesn't establish that low 5-HTP causes autism, measures symptom severity reliably, or identifies children who would benefit from supplementation.

Early Puberty

A urine-profiling study found lower 5-HTP in children with central precocious puberty. The researchers suggested increased conversion through the serotonin pathway, but they didn't directly measure that conversion rate.

In the same study, a seven-marker model that included 5-HTP identified about 93% of children with peripheral precocious puberty and correctly classified about 94% of healthy controls in its main analysis. Peripheral precocious puberty is a different form of early puberty from the central form. These figures describe the combined research model, and its performance was lower in a held-out subset. They aren't accuracy estimates for urinary 5-HTP alone.

Parkinson's Disease

An LC-MS/MS study measured 21 tryptophan-related compounds in urine from 41 people with Parkinson's disease and 20 controls. Urinary 5-HTP didn't differ significantly between the groups. The only compound with a clear group difference was indole-3-acetic acid.

That study used the same broad analytical approach as this test, but it didn't validate this laboratory's assay for diagnosis. A urinary 5-HTP result cannot confirm or exclude Parkinson's disease.

Serotonin-Producing Tumors

Some neuroendocrine tumors release serotonin or its precursors. Certain tumors produce 5-HTP because they have limited ability to convert it into serotonin. This explains interest in measuring upstream compounds, but urinary 5-HTP hasn't become an established standalone tumor test.

Clinical evaluation of suspected carcinoid syndrome commonly includes 5-HIAA testing. Carcinoid syndrome can cause flushing and diarrhea when a tumor releases active substances into the circulation. A normal 5-HIAA result doesn't exclude every neuroendocrine tumor, and an exploratory urinary 5-HTP result doesn't resolve that uncertainty.

A plasma study compared 26 people with carcinoid syndrome with 20 healthy controls. A ratio combining compounds from the serotonin and kynurenine pathways detected about 92% of the cases, with no false positives among those controls. That finding belongs to a research plasma model. It wasn't the performance of urinary 5-HTP or of a three-compound panel containing only 5-HTP, serotonin, and 5-HIAA.

What Blood Studies Add

A small study of untreated high blood pressure found blood 5-HTP about 30% higher than in controls, alongside lower serotonin. This pattern suggests a question about metabolism; it doesn't prove that the enzyme converting 5-HTP into serotonin is impaired.

In 62 people with glioblastoma, a lower serum 5-HTP-to-tryptophan ratio before surgery was associated with shorter median survival, about 12 months compared with 18 months. The study selected its dividing point from its own data. This was an association involving a blood ratio in people with an aggressive brain tumor.

In a pregnancy cohort, higher maternal serum 5-HTP early in pregnancy was associated with reduced embryonic growth. Neither this finding nor the other blood associations provides a personal risk estimate from a urine result.

When Results Can Be Misleading

• 5-HTP supplements: administered 5-HTP can change urinary excretion of the precursor and related compounds. A result during supplementation cannot be interpreted as your body's unassisted production, and it doesn't quantify how much of your dose you absorbed.
• Carbidopa: this medication inhibits conversion of 5-HTP to serotonin outside the brain. Human pharmacokinetic studies found changes in plasma 5-HTP and 5-HIAA after carbidopa pretreatment. They don't establish the size or direction of a change on this urine assay.
• Urine concentration and reporting: hydration affects the concentration of substances in urine. Normalization can partly address dilution, but results depend on what the laboratory uses as the denominator. The catalog's mcg/g label alone doesn't identify that denominator.
• Illness and kidney handling: the published studies show that disease and renal processing can affect these measurements. They don't provide correction factors that separate those effects from changes in production.
• Analytical effects: other substances in urine can suppress or enhance the signal during LC-MS analysis. Sample preparation, storage, calibration, and internal standards affect how well a laboratory controls these problems.

LC-MS separates compounds and identifies them by mass. It can distinguish closely related molecules when the method is properly validated, but the technique's name doesn't guarantee that different laboratories produce interchangeable numbers. An analytical error range reported for an entire research metabolite panel also isn't an estimate of this test's own precision.

Interpreting Change Over Time

Broader urine-metabolomics studies have measured technical and biological variation, but they don't establish the expected day-to-day variation or a meaningful change for this specific 5-HTP assay. Consistent collection and analysis can make comparisons easier to interpret. A change still cannot be assumed to mean improved serotonin function, mood, or sleep.