From the Guidelines
Blood test results are crucial in diagnosing and monitoring anaphylaxis, with elevated serum tryptase levels being the most specific indicator, and should be interpreted in conjunction with clinical symptoms. The most recent and highest quality study, 1, published in 2020, provides a comprehensive update on the diagnosis and management of anaphylaxis. According to this study, anaphylaxis is an acute, life-threatening systemic allergic reaction that may have a wide range of clinical manifestations.
Key Laboratory Findings
- Elevated serum tryptase levels (>11.4 ng/mL) measured within 3 hours of symptom onset are the most specific laboratory indicator of anaphylaxis, as tryptase is released from activated mast cells during the reaction 1.
- Histamine levels may also be elevated but must be measured within 30-60 minutes of reaction onset due to rapid metabolism 2.
- Complete blood count might show increased white blood cells, particularly neutrophils, during the acute phase.
- Specific IgE antibody tests can identify potential triggers like foods, medications, or insect venoms, though these don't confirm the acute reaction itself.
- Complement levels (C3, C4) may be decreased in certain forms of anaphylaxis.
Disease Progression and Monitoring
- Serial measurements of these markers, especially tryptase, help track disease progression, with declining levels indicating resolution 3.
- However, normal test results don't rule out anaphylaxis, as up to 50% of patients may have normal tryptase levels even during severe reactions.
- Blood tests should always be interpreted alongside clinical symptoms, as laboratory findings serve as supportive rather than definitive diagnostic criteria for anaphylaxis 1.
Clinical Considerations
- The NIAID/FAAN anaphylaxis diagnostic criteria, which include acute onset of illness with involvement of the skin, mucosal tissue, or both, with either respiratory involvement or reduced blood pressure and/or associated symptoms of end-organ dysfunction, can be helpful in diagnosing anaphylaxis 1.
- Epinephrine administration is not limited to those patients meeting the NIAID/FAAN diagnostic criteria, and clinical judgment plays a crucial role in managing anaphylaxis 1.
From the FDA Drug Label
The FDA drug label does not answer the question.
From the Research
Blood Test Results and Anaphylaxis
- Blood test results can provide valuable information about anaphylaxis, including the presence of elevated serum tryptase levels, which reflect mast cell degranulation 4.
- Serum tryptase levels can be used to support the clinical diagnosis of anaphylaxis when the diagnosis is not clear 4.
Disease Progression and Blood Test Results
- Blood test results can help identify individuals at risk of severe or fatal anaphylactic reactions, including those with coexisting asthma, mast cell disorders, older age, underlying cardiovascular disease, peanut and tree nut allergy, and drug-induced reactions 4.
- Monitoring of blood test results can also help identify potential biphasic reactions, which can occur in some individuals after an initial anaphylactic reaction 4, 5.
Treatment and Management
- The treatment of anaphylaxis involves the administration of intramuscular epinephrine, which can be delivered via an auto-injector or manual injection 6, 7, 8.
- Blood test results can help guide the management of anaphylaxis, including the use of adjunct medications such as histamine H1 and H2 antagonists, corticosteroids, beta2 agonists, and glucagon 4.
- The use of epinephrine auto-injectors has been shown to be effective in the treatment of anaphylaxis, and can help reduce barriers to epinephrine administration in emergency situations 6, 7, 8.