Tryptophan

Tryptophan too high

In adults without symptoms, a raised value of an amino acid is usually caused by a protein-rich meal or a protein shake shortly before the sample collection, by supplements containing amino acids (such as BCAAs, glutamine, arginine or taurine), or by the blood not being processed quickly enough. Reduced kidney function, liver disease, poorly controlled diabetes and some medicines can also raise values. A single, slightly raised value usually has no significance and causes no symptoms. Rarely, a strongly raised value, especially together with abnormalities in related amino acids, fits an inborn metabolic disease.

Tryptophan too low

A low value is usually caused by fasting, a low-protein meal or normal fluctuations during the day. Inflammation, serious illness and malnutrition can also lower tryptophan. A low value is not proof of a serotonin shortage in the brain or of low mood, and does not mean you need tryptophan as a supplement. A low value does not cause symptoms by itself.

Useful for

In hospitals, a specialist uses this test when a metabolic disorder is specifically suspected, or to monitor a known metabolic disease and the diet that goes with it. For adults without symptoms, to find nutritional deficiencies or to choose supplements, the test is not useful according to current knowledge. If you use protein supplements or single amino acids, you get a result that mainly shows that intake.

How common is it?

Inborn disorders of amino acid metabolism are rare. In the Netherlands, the heel prick finds on average about 12 children with PKU (phenylketonuria) per year and about 1 child with MSUD (maple syrup urine disease) or tyrosinemia type 1. There are no Dutch figures on abnormal amino acid values in adults without symptoms.

RIVM, heel prick screening (pns.nl)