Histamine, µg/24 hr, Urine measures the total amount of histamine eliminated in the urine during a 24-hour collection period. Histamine is an important signaling molecule in the immune system and is primarily stored in mast cells and basophils. When these cells are activated—such as during allergic reactions, inflammation, or immune responses—they release histamine into surrounding tissues and the bloodstream.
Histamine contributes to many familiar symptoms associated with allergies and immune activation. It can cause blood vessels to widen, increase vascular permeability, stimulate nerve endings, and affect gastrointestinal function. These effects can lead to symptoms such as itching, flushing, hives, nasal congestion, headaches, and digestive discomfort.
Because histamine levels in the bloodstream rise and fall quickly, measuring histamine in urine over a full day provides a broader picture of histamine production and release. The result is reported as micrograms of histamine excreted over 24 hours (µg/24 hr). The typical reference range for this test is 0–65 µg/24 hr, although ranges may vary slightly depending on the laboratory.
Healthcare providers may order this test when evaluating symptoms that could be related to excessive histamine activity. These may include:
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Recurrent flushing or unexplained skin redness
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Chronic itching or hives
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Allergic symptoms without a clear trigger
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Headaches or migraines
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Nasal congestion or sinus symptoms
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Abdominal pain, diarrhea, or bloating
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Episodes of rapid heart rate or low blood pressure
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Sensitivity to certain foods, alcohol, or medications
Elevated urinary histamine can be seen in several situations. Allergic reactions are one of the most common causes, as mast cells release histamine in response to allergens. Increased histamine may also occur in mast cell activation disorders, conditions where mast cells release excessive inflammatory mediators. Some individuals may also experience histamine intolerance, a condition in which the body has difficulty breaking down histamine due to reduced activity of enzymes such as diamine oxidase (DAO).
In rare cases, high histamine levels may be associated with certain tumors that produce histamine or with inflammatory gastrointestinal diseases.
Interpretation of urinary histamine results should always be considered alongside symptoms, medications, diet, and other laboratory findings. Additional testing—such as mast cell mediators, tryptase, or histamine metabolites—may be used to further evaluate abnormal results.
Understanding urinary histamine levels can help guide investigations into chronic allergy-like symptoms, unexplained inflammatory reactions, and possible mast cell–related conditions.
Histamine, µg/24 hr, Urine
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