Tryptase Does Not Reliably Distinguish Food-Related from Non-Food-Related Anaphylaxis
Obtaining tryptase levels will not effectively determine whether anaphylaxis is food-related versus triggered by other causes, as tryptase elevation correlates with severity of the reaction rather than the specific trigger, and remains normal in a substantial proportion of food-induced anaphylaxis cases. 1
Why Tryptase Cannot Identify the Trigger
Tryptase reflects mast cell degranulation intensity, not the allergen source. The level correlates with severity of anaphylaxis across all triggers rather than identifying whether the cause is food, drug, venom, or idiopathic. 1
Food-induced anaphylaxis frequently shows no tryptase elevation. Serum tryptase is elevated less often in food allergy compared to other triggers, making it particularly unreliable for confirming food as the cause. 2
Tryptase remains normal in 36-60% of confirmed anaphylaxis cases. Even when anaphylaxis is definitively diagnosed by clinical criteria, tryptase fails to rise in a substantial proportion of patients, with no change between acute and baseline levels. 1
Drug-induced anaphylaxis shows higher tryptase levels than food-induced reactions. When comparing triggers, drugs cause both more severe anaphylaxis and higher tryptase concentrations than foods at both acute (T1) and baseline measurements, but this doesn't help identify the trigger prospectively. 1
What Tryptase Actually Tells You
Tryptase elevation indicates severity, not etiology. Higher tryptase levels correlate positively with grades of anaphylaxis severity (r = 0.49, p < 0.001), being more frequently elevated in severe reactions regardless of cause. 1
Acute tryptase peaks 1-2 hours after symptom onset. Measurement should occur within this window, as levels decline by 4-6 hours and normalize by 12-24 hours, making timing critical for any diagnostic utility. 1
Baseline tryptase helps distinguish systemic mastocytosis from idiopathic anaphylaxis. An elevated baseline tryptase (>20 ng/mL) when asymptomatic suggests systemic mastocytosis rather than typical anaphylaxis, with a beta-tryptase to total tryptase ratio >20 in mastocytosis versus ≤10 in idiopathic anaphylaxis. 3
The Correct Diagnostic Approach for Identifying Food Triggers
Detailed clinical history remains the primary diagnostic tool. The history should concentrate on all agents encountered before the reaction, with special attention to timing (food reactions typically occur within minutes to hours of ingestion). 3
Skin testing to specific foods is the test of choice. When food allergy is suspected, skin prick testing followed by intradermal testing if needed provides the most useful diagnostic information, though standardized food extracts are not always available and fresh food extracts may be required. 3
Serum food-specific IgE testing serves as an adjunct. In vitro testing for food-specific IgE antibodies can supplement skin testing but should not replace it as the primary diagnostic modality. 3
Oral food challenges provide definitive diagnosis when history and testing are equivocal. Double-blind placebo-controlled food challenges performed in a medical facility by experienced personnel can definitively identify or exclude specific food triggers. 3
Critical Pitfalls to Avoid
Do not rely on tryptase to rule out food allergy. A normal tryptase during an anaphylactic episode does not exclude food as the trigger, as food-induced reactions commonly show no tryptase elevation. 2, 1
Do not assume elevated tryptase confirms a specific trigger. Tryptase elevation only confirms mast cell activation occurred; it provides no information about whether the cause was food, medication, venom, or another trigger. 1
Timing of tryptase measurement is critical if obtained. Samples must be drawn 1-2 hours after symptom onset for optimal sensitivity; later measurements will likely be normal even in true anaphylaxis. 1
When Tryptase Measurement Is Actually Useful
When the clinical diagnosis of anaphylaxis itself is uncertain. Tryptase can help confirm that mast cell degranulation occurred when the presentation is atypical or the diagnosis is questioned. 4
To screen for underlying systemic mastocytosis. Obtaining both acute and baseline tryptase levels helps identify patients who may have an underlying mast cell disorder predisposing them to severe reactions. 3, 5
In idiopathic anaphylaxis after excluding identifiable triggers. When intensive evaluation including food testing fails to identify a cause, tryptase patterns can help distinguish idiopathic anaphylaxis from systemic mastocytosis. 3