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Table 2 Criteria proposed to define mast cell activation disease (for references, see text).

From: Mast cell activation disease: a concise practical guide for diagnostic workup and therapeutic options

Criteria to define mast cell activation syndrome WHO criteria to define systemic mastocytosis
Major criteria Major criterion
1. Multifocal or disseminated dense infiltrates of mast cells in bone marrow biopsies and/or in sections of other extracutaneous organ(s) (e.g., gastrointestinal tract biopsies; CD117-, tryptase- and CD25-stained) Multifocal dense infiltrates of mast cells (>15 mast cells in aggregates) in bone marrow biopsies and/or in sections of other extracutaneous organ(s) (CD117-, tryptase- and CD25-stained)
2. Unique constellation of clinical complaints as a result of a pathologically increased mast cell activity (mast cell mediator release syndrome)  
Minor criteria Minor criteria
1. Mast cells in bone marrow or other extracutaneous organ(s) show an abnormal morphology (>25%) in bone marrow smears or in histologies 1. Mast cells in bone marrow or other extracutaneous organ(s) show an abnormal morphology (>25%) in bone marrow smears or in histologies
2. Mast cells in bone marrow express CD2 and/or CD25 2. Mast cells in bone marrow express CD2 and/or CD25
3. Detection of genetic changes in mast cells from blood, bone marrow or extracutaneous organs for which an impact on the state of activity of affected mast cells in terms of an increased activity has been proved. 3. c-kit mutation in tyrosine kinase at codon 816 in mast cells in extracutaneous organ(s)
4. Evidence of a pathologically increased release of mast cell mediators by determination of the content of 4. Serum total tryptase >20 ng/ml (does not apply in patients who have associated hematologic non-mast-cell lineage disease)
   • tryptase in blood  
   • N-methylhistamine in urine  
   • heparin in blood  
   • chromogranin A in blood  
   • other mast cell-specific mediators (e.g., leukotrienes, prostaglandin D2)  
  1. The diagnosis mast cell activation syndrome is made if both major criteria or the second criterion and at least one minor criterion are fulfilled. According to the WHO criteria [1], the diagnosis systemic mastocytosis is established if the major criterion and at least one minor criterion or at least three minor criteria are fulfilled.