Our MCAS medical brochure has been developed in collaboration with medical specialists in mast cell disorders. It includes the latest published consensus findings for diagnosing MCAS, alongside patient case examples and information on medical management.
We believe these resources will be helpful in understanding MCAS and providing practical advice for diagnosis and treatment of mast cell activation syndrome.
The three major forms of mast cell diseases are mastocytosis, mast cell activation syndrome (MCAS), and hereditary alpha tryptasemia syndrome (HαTs).
MCAS can be categorised as primary, secondary or idiopathic. Primary MCAS (known as monoclonal mast cell activation disorder) falls under the primary mast cell disorders category alongside systemic and cutaneous mastocytosis. These disorders are characterised by hyperproliferative mast cells. On the other hand, secondary and idiopathic MCAS are non-clonal. Secondary MCAS occurs due to IgE-mediated or non-IgE mediated allergic reactions while idiopathic MCAS refers to MCAS in which no allergic or autoimmune cause can be found.
HαTs is a recently recognised condition. It commonly leads to elevated serum tryptase levels due to an increased copy number of the TPSAB1 gene.
Weiler CR, Austen KF, Akin C, et al. AAAAI Mast Cell Disorders Committee Work Group Report: Mast cell activation syndrome (MCAS) diagnosis and management. J Allergy Clin Immunol. 2019;144(4):883-896.26.05.2021
Theoharides TC, Tsilioni I, Ren H. Recent advances in our understanding of mast cell activation–or should it be mast cell mediator disorders?. Expert review of clinical immunology. 2019 Jun 3;15(6):639-56.26.05.2021
Afrin LB, Ackerley MB, Bluestein LS, et al. Diagnosis of mast cell activation syndrome: a global" consensus-2". Diagnosis (Berlin, Germany). 2020 Apr 22.26.05.2021
Weiler CR. Mast cell activation syndrome: tools for diagnosis and differential diagnosis. The Journal of Allergy and Clinical Immunology: In Practice. 2020 Feb 1;8(2):498-506.26.05.2021
The coding of MCAS into the ICD-10 (American version) is an important step in gaining better recognition of MCAS.02.12.2016
Butterfield J, Weiler CR. The utility of measuring urinary metabolites of mast cell mediators in systemic mastocytosis and mast cell activation syndrome. The Journal of Allergy and Clinical Immunology: In Practice. 2020 Sep 1;8(8):2533-41.26.05.2021
Sheffield Protein Reference Unit tests for mast cell activation markers14.08.2017
24-hour urine samples are recommended for assessing MCAS as mast cell mediators with short half lives may show normal results in spot urine samples.
Samples must be kept chilled throughout collection, storage and transport as many mast cell mediators are thermolabile.
Multiple tests are often conducted; ideally two abnormal biochemical values are required to diagnose MCAS.
MCAS patients may not have raised mast cell mediator levels unless they are symptomatic.
A positive result does not confirm MCAS, and a negative result is insufficient to rule out MCAS. Alongside test results, other diagnostic evidence should always be considered.
Theoharides TC, Valent P, Akin C. Mast Cells, Mastocytosis, and Related Disorders. N Engl J Med. 2015;373(2):163-72.
Theoharides TC, Tsilioni I, Ren H. Recent advances in our understanding of mast cell activation - or should it be mast cell mediator disorders?. Expert Rev Clin Immunol. 2019;15(6):639-656. doi:10.1080/1744666X.2019.1596800
[A table of mast cell-derived mediators. While some mediators are preformed and stored in granules, others are synthesised de novo. Source: Castells 2006, Theoharides et al. 2019.]
[A diagram showing the different symptoms associated with MCAS and the mast cell-derived mediators driving these symptoms. Figure adapted from Theoharides et al. 2015.]
[A diagram showing the pathways by which mast cell-derived mediators are released. Upon recognition of endogenous and exogenous products by receptors, mast cells release mediators through one of several pathways: (1) degranulation and release of granules containing mediators such as histamine; (2) release of newly synthesized lipid mediators such as PGD2; (3) release of de novo-synthesized mediators such as cytokines; (4) release of extracellular vesicles, for example, exosomes. Figure taken from Dahlin et al. 2021.]
The following listed presentations are available to watch online and have been given by doctors and researchers across multiple disciplines who have specialised in MCAS.
Dr Ravi Sargur presents 'Urinary Mast Cell Mediators in Mast Cell Disorders' as part of the BSACI webinar series 2021
Dr Arnold Deering talks about MCAS with Samia Qader
The Royal College of GPs has developed an Ehlers Danlos Syndromes Toolkit that has a section on MCAS under Emerging Major Associations. The Toolkits have been created for primary healthcare professionals, patients and carers. These toolkits can be used to assist in the delivery of safe and effective care to patients.
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