Tryptase Elevation in Viral Infections

Understanding Tryptase Elevation

Up to 40% of patients with postural orthostatic tachycardia syndrome (POTS) report a viral upper respiratory or gastrointestinal infection as the precipitating event to their symptoms, suggesting that viral infections can trigger mast cell activation pathways 1
The COVID-19 virus specifically has been associated with both acute and long COVID-related POTS and potential mast cell activation, with evidence of neuronal tropism and angiotensin converting enzyme 2 depletion that may contribute to autonomic dysfunction 1
Infections and febrile illnesses are recognized triggers for mast cell activation in susceptible individuals 2

During acute anaphylaxis or mast cell activation, β-tryptase peaks at approximately 1 hour after symptom onset and has a half-life of about 2 hours, returning to baseline within 5-6 hours 3, 4, 5, 6
Serum tryptase should be measured between 1-2 hours after symptom onset (but no longer than 6 hours) to capture acute elevation 5, 6
A baseline tryptase measurement must be obtained >24 hours after any acute event to establish the patient's true baseline level 7
The diagnostic criterion requires an increase in serum tryptase of 20% + 2 μg/L above the individual's baseline level 1
A rise in serum tryptase indicates mast cell degranulation but does not discriminate between allergic and non-allergic triggers, including viral infections 3, 4

Tryptase <15 ng/mL is generally considered normal 7
Persistently elevated baseline tryptase >20 μg/L (measured when asymptomatic) is a minor diagnostic criterion for systemic mastocytosis and warrants bone marrow evaluation 6, 7
Tryptase >200 ng/mL indicates high mast cell burden and requires urgent hematology referral 6, 7

Treat any anaphylactic symptoms with epinephrine 0.3-0.5 mg intramuscularly as first-line therapy 5
Initiate H1 antihistamines (e.g., diphenhydramine) and H2 antihistamines (e.g., ranitidine or famotidine) for symptomatic relief 6
Consider leukotriene inhibitors if abdominal symptoms or flushing are prominent 6
Obtain a baseline tryptase level at least 24 hours after symptom resolution to determine if elevation was acute or represents an elevated baseline 7
If baseline remains >20 μg/L on repeat testing, proceed with workup for systemic mastocytosis including bone marrow biopsy with immunohistochemistry and KIT D816V mutation testing 6

Patients with documented MCAS or systemic mastocytosis should carry two epinephrine auto-injectors at all times 6
Serial tryptase monitoring every 3-6 months is recommended once diagnosis is established 6
Maintain a symptom diary to identify personal triggers, as viral infections may unmask underlying mast cell disorders 2

Normal tryptase does not exclude anaphylaxis or mast cell activation, as anaphylaxis can occur via basophil or complement activation pathways that do not release mast cell tryptase 3, 4
The connection between viral infections and mast cell activation is generally inconclusive except in rare monogenic disorders, making biomarker documentation during symptomatic episodes essential 2