From the Guidelines
Histamine tests, such as plasma histamine levels and urinary histamine metabolites, should be used to diagnose anaphylaxis, with plasma histamine levels measured between 10 minutes and 1 hour after the onset of symptoms, and urinary histamine metabolites measured up to 24 hours after the onset of symptoms 1. When diagnosing anaphylaxis, it is essential to consider the timing of the test, as plasma histamine levels begin to increase within 5 to 10 minutes of the onset of symptoms and remain increased for 30 to 60 minutes. Some key points to consider when using histamine tests include:
- Plasma histamine levels are not helpful if the patient is seen more than an hour after the onset of the event 1
- Urinary histamine metabolites, including methylhistamine, may be found for up to 24 hours after the onset of anaphylaxis 1
- Blood samples for measurement of tryptase levels are optimally obtained 15 minutes to 3 hours after symptom onset 1
- A serial measurement of tryptase levels during an anaphylactic episode followed by a baseline tryptase level after recovery of the event is more useful than a single measurement 1
- Normal levels of either tryptase or histamine do not rule out the clinical diagnosis of anaphylaxis 1 It is crucial to consult with an allergist or immunologist to determine the most appropriate test for specific symptoms and medical history, as proper diagnosis is essential for developing an effective treatment plan. In terms of treatment, options may include antihistamines, DAO enzyme supplements, or dietary modifications, and the choice of treatment will depend on the individual patient's needs and circumstances. Overall, histamine tests should be used in conjunction with clinical judgment and other diagnostic tools to diagnose and manage anaphylaxis effectively 1.
From the Research
Histamine Tests
- Histamine tests can be used to diagnose histamine intolerance, a condition that results from an imbalance between histamine intake and degradation 2.
- The histamine 50-skin-prick test is a tool that can be used to diagnose histamine intolerance, with a wheal size of ≥3 mm after 50 minutes indicating slowed histamine degradation 2.
- This test has been shown to be effective in distinguishing between individuals with histamine intolerance and those without, with 64 out of 81 individuals with histamine intolerance presenting with a histamine wheal ≥3 mm after 50 minutes, compared to only 14 out of 75 controls 2.
Anaphylaxis Diagnosis
- Anaphylaxis is a severe, life-threatening, systemic allergic reaction that is almost always unanticipated and may lead to death by airway obstruction or vascular collapse 3, 4, 5, 6.
- The diagnosis of anaphylaxis is typically made when symptoms occur within one hour of exposure to a specific antigen, and is based on clinical presentation rather than laboratory tests 3, 4, 5, 6.
- Serum histamine and tryptase levels can be used as confirmatory tests, but are difficult to interpret due to strict time considerations for blood sample collection 3, 5.
Treatment and Management
- The treatment of anaphylaxis involves the administration of intramuscular epinephrine, followed by supportive care for the patient's airway, breathing, and circulation 3, 4, 5, 6.
- Histamine H(1) receptor antagonists and corticosteroids may be useful adjuncts in the treatment of anaphylaxis, but should only be considered after epinephrine administration 3, 4, 5, 6.
- Patients with a history of anaphylaxis should be educated about their condition, including trigger avoidance and the correct use of epinephrine autoinjector kits 3, 4, 5, 6.