Short answer · Medically reviewed summary · Last updated: 2026-04-06
The ICD-10-CM code for Mastocytosis is Q82.2, while Mast Cell Activation Syndrome (MCAS) is typically coded under D89.40 (idiopathic mast cell activation syndrome), and both conditions previously fell under the ICD-9 code 757.33. Navigating Diagnostic Coding for Mast Cell Disorders As a clinician, I understand that navigating the coding system for Mastocytosis and MCAS can be frustrating, as these codes are essential for insurance authorization and clinical documentation. While Mastocytosis is a distinct group of disorders characterized by the abnormal accumulation of mast cells, MCAS is a functional disorder where mast cells release excessive mediators without necessarily having an abnormal cell count.
1 people with Mastocytosis and MCAS have shared their first-person experience on this question at DiseaseMaps.
ICD10 code of Mastocytosis and MCAS and ICD9 code
ICD-10 and ICD-9 codes for Mastocytosis and MCAS, with classification details for clinicians, coders and patients.
The ICD-10-CM code for Mastocytosis is Q82.2, while Mast Cell Activation Syndrome (MCAS) is typically coded under D89.40 (idiopathic mast cell activation syndrome), and both conditions previously fell under the ICD-9 code 757.33.
Navigating Diagnostic Coding for Mast Cell Disorders
As a clinician, I understand that navigating the coding system for Mastocytosis and MCAS can be frustrating, as these codes are essential for insurance authorization and clinical documentation. While Mastocytosis is a distinct group of disorders characterized by the abnormal accumulation of mast cells, MCAS is a functional disorder where mast cells release excessive mediators without necessarily having an abnormal cell count. In the ICD-10 system, Mastocytosis is classified under Q82.2, which covers various forms including cutaneous and systemic variants. Conversely, MCAS is classified under the D89.4 series, which allows for more specific coding based on the clinical presentation, such as D89.41 (monoclonal mast cell activation syndrome) or D89.42 (secondary mast cell activation syndrome).
Clinical and Practical Implications
For patients within our DiseaseMaps community, receiving an accurate diagnosis is the first step toward effective symptom management. Because Mastocytosis and MCAS can present with multisystem symptoms—ranging from dermatological flushing to severe gastrointestinal distress—precise coding is vital to ensure that your medical team can coordinate care effectively. We recognize that the diagnostic journey can feel isolating, especially when codes seem to shift or overlap. Please know that having these specific ICD-10 codes in your medical record is a tool to advocate for the specialized care you deserve. It is important to work closely with your immunologist or hematologist to ensure that your specific clinical manifestations are documented accurately, as this impacts both your treatment plan and your interactions with healthcare systems.
Medical Disclaimer: This information is provided for educational purposes only and does not constitute medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition.
References
- NIH Genetic and Rare Diseases Information Center (GARD) - Mastocytosis
- Orphanet: The portal for rare diseases and orphan drugs
- World Health Organization (WHO) ICD-10 Browser
- American Academy of Allergy, Asthma & Immunology (AAAAI)
Posted Sep 30, 2017 by Meredith 2000
