Is serum tryptase level useful in diagnosing anaphylaxis in patients in the Emergency Department (ED)?

From the Guidelines

Serum tryptase level testing is useful for anaphylaxis patients in the emergency department, but with important limitations, as it should be obtained within 1 to 2 hours after symptom onset for optimal results, and elevated tryptase levels support a diagnosis of anaphylaxis, particularly in cases with unclear presentation 1.

Key Considerations

• The test should be obtained within a specific time frame after symptom onset for optimal results, with the best time to measure serum tryptase levels being between 1 to 2 hours but no longer than 6 hours after the onset of symptoms 1.
• Elevated tryptase levels (>11.4 ng/mL or >2 times the baseline) support a diagnosis of anaphylaxis, particularly in cases with unclear presentation.
• However, tryptase testing should never delay emergency treatment of anaphylaxis, which remains a clinical diagnosis requiring immediate intervention with epinephrine (0.3-0.5 mg IM for adults, 0.15-0.3 mg for children) 1.
• Importantly, normal tryptase levels do not rule out anaphylaxis, as up to 50% of anaphylaxis cases show normal levels, especially in food-triggered reactions.
• The primary value of tryptase testing is for retrospective confirmation, allergy specialist follow-up, and identifying patients with mastocytosis who may have higher baseline levels.

Limitations and Potential Biases

• The evidence is based on studies from 2005 and 2020, with the most recent study providing a practice parameter update, systematic review, and grading of recommendations, assessment, development and evaluation (GRADE) analysis 1.
• The studies suggest that tryptase testing is not a definitive diagnostic tool, but rather a supportive test that can aid in the diagnosis of anaphylaxis.
• The evidence also highlights the importance of prompt treatment with epinephrine, regardless of tryptase levels, and the need for emergency physicians to prioritize treatment based on clinical presentation rather than waiting for tryptase results.

Clinical Implications

• Emergency physicians should be aware of the limitations and potential biases of tryptase testing in the diagnosis of anaphylaxis.
• The test should be used in conjunction with clinical presentation and other diagnostic tools to support a diagnosis of anaphylaxis.
• Prompt treatment with epinephrine remains the cornerstone of anaphylaxis management, and tryptase testing should not delay this treatment.

From the Research

Serum Tryptase Level in Diagnosing Anaphylaxis

• Serum tryptase level is a biomarker that has been studied for its potential in diagnosing anaphylaxis in patients in the Emergency Department (ED) 2, 3, 4, 5, 6.
• The studies suggest that while serum tryptase level can be useful in diagnosing anaphylaxis, it has limitations and should not be used as the sole diagnostic criterion 2, 4, 6.

Diagnostic Accuracy of Serum Tryptase Level

• A study found that peak tryptase concentrations were higher in anaphylaxis patients than in controls, but the test lacked sufficient sensitivity and specificity to establish a diagnosis of anaphylaxis in the ED 2.
• Another study found that serum baseline tryptase levels were higher in patients with severe anaphylaxis, suggesting that high tryptase levels may be associated with more severe anaphylaxis 3.
• A study reported that an acute serum tryptase level of more than 12.4 ng/mL had a high positive predictive value and specificity, but poor sensitivity and negative predictive value in an ED setting 6.

Limitations of Serum Tryptase Level

• Tryptase levels may not be raised in all cases of anaphylaxis, and in some cases, tryptase levels may not change significantly during an acute episode 4.
• The measurement of serum tryptase level may not be useful in differentiating anaphylactic from non-anaphylactic shock 2.
• The clinical utility of acute serum tryptase measurement in an ED setting may be limited by factors such as the timing of measurement and the lack of serial measurements 6.

Clinical Utility of Serum Tryptase Level

• Despite its limitations, serum tryptase level can be a useful biomarker in the diagnosis and management of anaphylaxis, particularly in cases where the diagnosis is uncertain or the patient has atypical symptoms 5.
• Serum tryptase level can be used in conjunction with other diagnostic criteria, such as clinical symptoms and physical findings, to support a diagnosis of anaphylaxis 5.