From the Guidelines
To test histamine levels, a 24-hour urine test for N-methylhistamine, a histamine metabolite, is the most comprehensive method, as it provides a view of histamine production over time 1. This approach is more reliable than measuring plasma histamine levels, which increase within 5-10 minutes of symptom onset but remain elevated for only 30-60 minutes 1. For accurate diagnosis, it's essential to consider the timing of sample collection, as serum tryptase levels peak 1-2 hours after symptom onset and can persist for up to 6 hours 1. In contrast, urinary histamine metabolites, such as methylhistamine, can be detected for up to 24 hours after the onset of anaphylaxis 1. Some key points to consider when testing histamine levels include:
- Blood tests for serum histamine levels require careful handling due to rapid fluctuations in levels 1
- A 24-hour urine test for N-methylhistamine provides a comprehensive view of histamine production over time 1
- Skin prick tests can help identify allergic reactions but do not directly measure histamine levels 1
- Histamine testing is not standardized, and results should be interpreted by a healthcare provider alongside symptoms and medical history 1
- If you suspect histamine-related issues, consult with an allergist, immunologist, or gastroenterologist who specializes in histamine disorders rather than attempting self-diagnosis 1. It's crucial to note that normal levels of either tryptase or histamine do not rule out the clinical diagnosis of anaphylaxis, and these tests are not universally available or specific for anaphylaxis 1.
From the Research
Testing Histamine Levels
To test histamine levels, several methods can be employed, including:
- Urine tests: Histamine levels can be measured in urine, which may reflect plasma histamine levels 2. This method has several advantages, including stability, accessibility, and the opportunity for retrospective analysis.
- Blood tests: Plasma histamine levels can be measured using a sensitive radioenzymatic assay 3, 4. This method can be used to distinguish patients with mastocytosis from those with recurrent unexplained anaphylaxis.
- Ultra High Performance Liquid Chromatography and Fluorimetric detection (UHPLC-FL): This method can be used to determine histamine and methylhistamine in human urine 5.
Methods for Measuring Histamine
Different methods can be used to measure histamine levels, including:
- Cation-exchange chromatography, organic solvent extraction, o-phthalaldehyde condensation, and measurement of fluorescence 2
- Radioenzymatic assay 3, 4
- UHPLC-FL 5
- Histamine methyltransferase preparation from pig brain, of high activity tritiated S-adenosylmethionine, and of a heat precipitation step to reduce interference from plasma constituents 4
Normal Histamine Levels
Normal histamine levels can vary depending on the method used and the population being studied. Some reported normal levels include: