MAST CELL CODES
- Girl In A Bubble
- Sep 16, 2025
- 2 min read
D89.40 Mast cell activation, unspecified
D89.41 Monoclonal mast cell activation syndrome
D89.42 Idiopathic mast cell activation syndrome
D89.43 Secondary mast cell activation
D89.49 Other mast cell activation disorder
ICD-10 CODES for MCAS
Patients are constantly looking to give this info to doctors here are the codes and the coding links . Here is a full explanation of the codes: D89.40 Mast cell activation, unspecified
The code, "MCAS, Unspecified", is used when information in a patient's medical record is not sufficient to allow for selection of the current MCAS diagnoses. Researchers recognize that readily available, current diagnostic methods for determining a rise in mast cell mediators after a symptomatic episode (one of the required co-criterion for identifying a mast cell activation event) are not ideal and for some patients who present with typical and recurrent signs and symptoms of mast cell activation, are still not detectable as elevated. Non-specialist physicians may most commonly use serum tryptase levels, but more often than not tryptase will not prove diagnostic.
D89.41 Monoclonal mast cell activation syndrome
Monoclonal MCAS (MMAS):
Also called clonal mast cell activation syndrome , a harbinger to SM , what you need to know
Key points;
These patients meet 1-2 criteria for SM
Spindle shape mast cells
Usually normal tryptase
This code is used when a patient meets one or two criteria for systemic mastocytosis,
D89.42 Idiopathic mast cell activation syndrome
Idiopathic MCAS is proposed as a final diagnosis after proposed mast cell activation criteria have been fulfilled and a thorough evaluation has excluded the possibility of another underlying cause for this activation
D89.43 Secondary mast cell activation
Secondary MCAS occurs when mast cells are normal in function and quantity , but respond to external stimulus, including, allergens , antibodies, and many other stimuli .
D89.49 Other mast cell activation disorder
The proposed code, "MCAS, Other", would be used when none of the above-mentioned proposed diagnoses for MCAS are applicable, for example for a new emerging MCAD disease category
Minor SM criteria
1) 25% of all MCs are atypical cells (type I or type II) on
BM smears or are spindle-shaped in MC infiltrates
detected on sections of visceral organ
2) KIT
point mutation at codon 816 in the BM or another
extra cutaneous organ
3). MCs in BM or blood or another extra cutaneous organ
exhibit CD2 and/or CD25
4) Baseline serum tryptase level > 20 ng/mL important ; Of note, the serum tryptase criterion does not apply to patients with an associated clonal hematologic non mast cell lineage disorder (AHNMD), since tryptase in such patients can originate from myeloid precursor cells.
* If at least 1 major and 1 minor or
3 minor SM criteria are fulfilled, the diagnosis of SM
can be obtained
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