Histidine

Histidine is an essential amino acid, a building block of proteins that your body cannot make and must obtain from food. A histidine test measures the amount of this amino acid in your blood or urine, often as part of a broader amino acid profile.

Histidine participates in many processes, including protein synthesis, tissue repair, and serving as a precursor to histamine, a compound involved in immune responses. Levels can be influenced by nutrition, growth, and how your body breaks down and clears amino acids.

Your clinician may order histidine testing to evaluate for inherited metabolic conditions such as histidinemia, to assess nutritional status, or to help investigate concerns related to liver or kidney function. It can also be used to monitor people receiving specialized diets or intravenous nutrition, or to interpret abnormal newborn screening or developmental concerns.

Because histidine is linked to the production of histamine and to protein metabolism, unusual results can provide clues about inflammation, immune activity, or tissue breakdown. Paired with other amino acids and clinical findings, the result helps guide whether additional testing, dietary changes, or genetic evaluation is needed.

Histidine results are interpreted in the context of your age, the specimen type (plasma or urine), and the testing method. Your healthcare team will usually look at the overall amino acid pattern rather than a single value in isolation.

Higher values can be seen with an inherited enzyme deficiency affecting histidine breakdown, high dietary intake or supplementation, reduced kidney clearance, or increased tissue turnover. Lower values can reflect poor intake, malabsorption, chronic inflammation, or increased demand during rapid growth. If a result is unexpected, your clinician may repeat the test, review medications and diet, and consider follow‑up studies such as metabolic or genetic evaluations, as well as checks of kidney and liver function.