Diagnosing MCAS requires a systematic, stepwise approach, which means that it can take a considerable amount of time to receive a formal diagnosis of MCAS.
If some, but not all, of these steps have been undertaken people are frequently considered to have a diagnosis of suspected MCAS:
The first step is recognising the presence of typical clinical symptoms across multiple body systems.
MCAS symptoms are often episodic or wax and wane (meaning that they go and come back) and their severity can fluctuate over time.
Symptoms can include:
Another step in the diagnosis of MCAS is often referred to as a ‘test of treatment’. It is underpinned by the theory that, if a person responds to MCAS treatment, this is evidence to suggest that the individual has MCAS.
Please seek medical support:
Some of the medicines mentioned in this list are available over the counter from the pharmacist, but many require a prescription from your doctor. We would recommend that you seek medical guidance either from a pharmacist or other medical health professional when using any of these medicines to manage the symptoms of MCAS.
Common medications that can be used for MCAS include:
Ideally, the previous steps are combined with a biochemical assessment to show evidence of elevated mediator release from mast cells.
Finally, it is important to discount other potential diagnoses, or determine whether an individual is suffering multiple conditions (with or without MCAS).
Conditions which should be considered, include other causes of anaphylaxis, autoimmune diseases, autoinflammatory conditions, vasculitis or Addison’s.
This stepwise process is reflected in the published diagnostic criteria for the condition (Molderings et al., 2011; Valent et al., 2019) and in the diagnostic algorithm proposed by Giannetti et al., 2021). If a person fulfils each of these four sets of criteria, a confident MCAS diagnosis can be provided. Frequently this process requires a ‘trial and error’ approach, and people may have to wait a long time for a definitive diagnosis. The uncertainty of this situation can be very difficult for people who suspect that they have MCAS but have not had their condition diagnosed. If you have been affected by this, please do reach out for further information and support from the charity.
If you are a medical professional and would like to access more information related to MCAS diagnosis, please see the Diagnostic Support section of the Resources for Medical Professionals page, and the MCAS Bibliography.
Weiler CR. Mast Cell Activation Syndrome: Tools for Diagnosis and Differential Diagnosis. J Allergy Clin Immunol Pract. 2020;8(2):498-506.
The following papers are key resources for diagnostic tests.
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
Sign up to become a Friend of Mast Cell Action so we can keep you up to date on our progress and on how to get involved in our latest campaigns and initiatives. Please click on Data Protection at the bottom of the page to see our Data Protection Information.
Mast Cell Action relies entirely on the generosity of people like you. Please make a donation now and together we can make a difference for sufferers of MCAS.