Tryptophane (blood)

This test measures the amount of tryptophan, an essential amino acid, in your blood. Tryptophan is a building block for proteins and a precursor for several important molecules, including serotonin, melatonin, niacin, and metabolites in the kynurenine pathway that influence immune function.

It is usually performed on a plasma or serum sample, sometimes after a brief fast, and may be ordered alone or as part of a broader amino acid profile. Because tryptophan availability reflects both diet and metabolism, the test helps your provider see how your body is using and processing amino acids.

Tryptophan levels can provide clues about nutrition, absorption, and metabolism. Low values may occur with poor intake, malabsorption, or inherited transport or metabolic conditions such as Hartnup disorder. Levels can also shift in chronic inflammation or autoimmune activity, where the body diverts tryptophan into immune-related pathways, which may indirectly affect mood, sleep, and energy.

Your clinician may order this test if you have symptoms suggesting an amino acid imbalance, unexplained rashes or neurologic issues, growth concerns in children, chronic diarrhea, or concerns about excessive supplement use. It can help guide nutrition plans, monitor therapy in metabolic disorders, and give context alongside other labs that assess liver, kidney, and immune status.

Your results are interpreted using age-specific reference intervals and your clinical context. A value below the expected range may point to inadequate intake, malabsorption, increased use by the body during illness, or a transport or metabolic disorder. A value above the expected range can be related to high protein intake, supplement use, or reduced clearance, and sometimes appears with certain medications or health conditions.

If your result is outside the expected range, your provider may review your diet, supplements, and medicines; check related amino acids or vitamin markers; or order follow-up tests that look at inflammation or downstream metabolites. Decisions about treatment or further testing are based on your symptoms, history, and other laboratory findings, not this result alone.