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  • Signs and symptoms of mast cell activation that involve at least two organ systems and may include abdominal pain, diarrhea, flushing, headache, and concentration difficulties.

  • No other medical disorder better explains these signs and symptoms.

  • Objective evidence of mast cell activation while symptomatic including elevated levels of tryptase on a blood test, and/or elevated levels of mast cell metabolites including histamine and/or prostaglandin in a 24-hour urine specimen.

  • Reduced symptoms with medications that block mast cell mediators such as antihistamines, cromolyn, and leukotriene antagonists.


  • Symptoms of mast cell activation as stated previously as well as specific clinical manifestations such as anaphylaxis and evidence of organ dysfunction, organ enlargement, and/or unexplained bone disease in more aggressive forms.

  • Characteristic physical examination findings particularly urticaria pigmentosa.

  • Serum tryptase >20 ng/mL or >11.4 ng/mL in patients with characteristic signs and symptoms of mastocytosis including anaphylaxis.

  • Documentation of abnormal clustering such as aggregates or sheets of mast cells on a bone marrow or extracutaneous biopsy (eg, liver, intestine).

  • Demonstration of a clonal mast cell population such as abnormal cell morphology (eg, spindle forms), specific cell surface marker expression (eg, CD2, CD25), and/or positive mutational analysis (eg, D816V mutation on the mast cell KIT gene).


Mast cell disorders are increasingly recognized as a cause of chronic abdominal symptoms. Interestingly, the presenting signs and symptoms of mast cell activation are seen in all the types of mast cell disorders including disorders where abnormal clonal mast cells can be identified (eg, systemic mastocytosis) and disorders where the mast cells are believed to be nonclonal but with abnormal activation (eg, mast cell activation syndrome) (see Classification section for more details). Any of these patients may complain of abdominal pain, diarrhea, nausea and vomiting, reflux, and bloating. Patients with systemic mastocytosis may additionally be at risk for peptic ulcer disease, and in the more aggressive stage portal hypertension and intestinal malabsorption.

A thorough history and physical examination is necessary to illicit the signs and symptoms of mast cell activation (see Clinical Findings section). Objective evidence of mast cell activation can be obtained with various laboratory tests and further testing should be performed to further differentiate between the various disorders that present with mast cell activation. Once the diagnosis is suspected and other medical disorders have been ruled out, patients should undergo a trial of anti–mast cell mediator and mast cell stabilizer medications with a plan to carefully assess treatment response. Depending on the type of mast cell disorder, specific treatments and further testing may be warranted. The correct diagnosis of a mast cell disorder may lead to specific treatment with excellent symptom relief, improved quality of life, and prevention of unnecessary tests and procedures.


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