From the Guidelines
Tryptase levels should be measured between 1 to 2 hours after the onset of suspected anaphylaxis symptoms, and no later than 6 hours, for optimal diagnostic value. This timing is crucial because serum tryptase levels peak 60-90 minutes after the onset of anaphylaxis and persist for up to 6 hours 1. Measuring tryptase levels within this timeframe can help establish the diagnosis of anaphylaxis, particularly when caused by insect stings or parenteral medications. It's essential to note that normal tryptase levels do not rule out anaphylaxis, especially in food-induced reactions where elevations are less common.
The diagnosis of anaphylaxis can be challenging, and laboratory tests, including tryptase levels, should be used in conjunction with clinical judgment and established diagnostic criteria, such as the NIAID/FAAN criteria 1. These criteria propose that anaphylaxis is likely when one of three criteria are fulfilled, including acute onset of illness with involvement of the skin, mucosal tissue, or both, with either respiratory involvement or reduced blood pressure, among other symptoms.
In addition to tryptase levels, other laboratory tests, such as plasma histamine and urinary histamine metabolites, may be helpful in establishing the diagnosis of anaphylaxis 1. However, the timing of these tests is critical, as plasma histamine levels begin to increase within 5-10 minutes of symptom onset and remain elevated for only 30-60 minutes.
It's also important to consider the different forms of tryptase, including alpha-tryptase and beta-tryptase, which can help distinguish between systemic anaphylaxis and degranulation of mast cells related to mastocytosis 1. A ratio of total tryptase to beta-tryptase can be useful in making this distinction, with a ratio of 10 or less indicative of an anaphylactic episode not related to systemic mastocytosis.
Overall, measuring tryptase levels between 1 to 2 hours after symptom onset, and considering other laboratory tests and clinical criteria, can help establish the diagnosis of anaphylaxis and guide treatment decisions.
From the Research
Measuring Tryptase Levels in Suspected Anaphylaxis
- Tryptase levels should be measured as soon as possible after successful emergency treatment for anaphylaxis, with serum samples taken within 1-2 hours but no later than 4 hours from the onset of symptoms 2
- Measuring tryptase levels can help confirm the diagnosis of anaphylaxis, especially when the clinical diagnosis is not clear 3
- Two strategies for evaluating changes in tryptase levels have been proposed for diagnosing anaphylaxis, including establishing a threshold of tryptase levels during reaction exceeding 2 ng/mL + 1.2* (baseline tryptase levels) or a ratio of tryptase levels during reaction versus baseline tryptase exceeding a threshold of 1.685 4
Timing of Tryptase Measurement
- Serum tryptase levels should be measured within a specific time frame after the onset of anaphylaxis symptoms, as levels may decrease over time 2
- Elevated serum tryptase levels can occur during protracted anaphylaxis, even 96 and 120 hours after the onset of symptoms 5
- Baseline tryptase levels can be useful in identifying patients at increased risk of more severe anaphylaxis 6
Clinical Considerations
- Clinicians should consider measuring tryptase levels in patients with suspected anaphylaxis, especially when the diagnosis is unclear or when patients have a history of severe allergic reactions 3
- Patients with anaphylaxis should be monitored for a period of time after the onset of symptoms, typically 6-12 hours, due to the risk of relapse or biphasic reactions 2, 3