Haematology · Allergy and Immunology
WHO Diagnostic Criteria for Systemic Mastocytosis calculator
Enter the published formula inputs below to calculate and interpret this score.
Clinical inputs
Allowed range: 0–1000 ng/mL
Counts only when the value used is above 20 ng/mL. If hereditary alpha-tryptasemia is known, divide by 1 plus the extra gene copies.
Allowed range: 0–10 copies
Used only when hereditary alpha-tryptasemia is known. The printed example is 30 ng/mL with 2 extra copies: 30 divided by 3 equals 10.
Result
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Clinical inputs
- Major criterion
- Atypical or spindle-shaped mast cells
- Activating KIT mutation
- CD2, CD25, or CD30
- Baseline serum tryptase (ng/mL)Accepted range: 0 to 1000
- Unrelated myeloid neoplasm
- Known hereditary alpha-tryptasemia
- Extra alpha-tryptase gene copiesAccepted range: 0 to 10
Primary source
Khoury JD et al. The 5th edition of the World Health Organization Classification of Haematolymphoid Tumours: Myeloid and Histiocytic/Dendritic Neoplasms. Leukemia. DOI: 10.1038/s41375-022-01613-1. PMID: 35732831. The mastocytosis section states that CD30 expression and any KIT mutation causing ligand-independent activation were accepted as minor criteria, and that basal serum tryptase above 20 ng/mL, adjusted for hereditary alpha-tryptasemia, is a minor criterion, citing Valent et al. Valent P et al. Updated diagnostic criteria and classification of mast cell disorders: a consensus proposal. HemaSphere. DOI: 10.1097/HS9.0000000000000646. PMID: 34901755. Table 2: the major criterion is multifocal dense infiltrates of mast cells, at least 15 mast cells in aggregates, in bone marrow biopsies and/or sections of other extracutaneous organs. Minor criteria are: at least 25% of mast cells atypical (type I or type II) on marrow smears or spindle-shaped in infiltrates on sections; a KIT-activating point mutation at codon 816 or another critical region in marrow or another extracutaneous organ; mast cells in marrow, blood, or another extracutaneous organ expressing CD2 and/or CD25 and/or CD30; and baseline serum tryptase above 20 ng/mL. Tryptase does not count when an unrelated myeloid neoplasm is present. When hereditary alpha-tryptasemia is known, divide the basal tryptase by 1 plus the extra alpha-tryptase gene copies. The printed example is tryptase 30 ng/mL with 2 extra copies: 30/3 = 10, which is not a minor criterion. Unknown TPSAB1 status uses the unadjusted value. The diagnosis is systemic mastocytosis when at least 1 major and 1 minor criterion are fulfilled, or when 3 minor criteria are fulfilled. Footnote a excludes spindle-shaped mast cells that only line vessels, fat, nerve, or endosteum, and excludes atypical mast cells in or next to marrow particles on the smear. (2022)
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