In Primary MCAS, researchers theorize that the threshold for chemical mediator release, also called degranulation, is lower, meaning it takes less outside stimulation to cause a reaction.
In these cases, reactions occur as a result of IgE-mediated (an environmental allergen, such as food or medication) and non-IgE-mediated (such as exercise) mechanisms.
[15][16] Some examples of tissue specific consequences of mast cell activation include urticaria, allergic rhinitis, and wheezing.
Systemic mast cell activation presents with symptoms involving two or more organ systems (skin: urticaria, angioedema, and flushing; gastrointestinal: nausea, vomiting, diarrhea, and abdominal cramping; cardiovascular: hypotensive syncope or near syncope and tachycardia; respiratory: wheezing; naso-ocular: conjunctival injection, pruritus, and nasal stuffiness).
This can result from the release of mediators from a specific site, such as the skin or mucosal tissue, or activation of mast cells around the vasculature.
[18] A workshop in 2022 proposed three diagnostic criteria:[19] According to the American Academy of Allergy, Asthma, and Immunology (AAAI), the most precise method of diagnosing MCAS is through a bone marrow biopsy and aspirate.