We all have mast cells in our bodies. They are a normal part of our immune system. They are in our digestive system, airways, skin and other tissues. Mast cells can help fight off infections.

There are many diseases where mast cells are overactive including hay fever, food and drug allergies, asthma, and chronic hives. These diseases can be caused by common allergens. However, in many cases, there is no known trigger.

Some rare conditions where too many mast cells are present are:

  • mastocytosis

  • mast cell leukemia

Mast Cell Activation Syndrome (MCAS)

MCAS is a rare disorder that is not fully understood. A lot of research is ongoing to figure out the cause and best treatments for it. It is more likely to be in patients with many systemic allergic reactions or anaphylaxis.

As a new referral to our clinic, our goals are to diagnose and create a plan of care designed to ease symptoms.

MCAS diagnosis is based on:

  • Symptoms that result from overactive mast cells

  • How well medicines work to target mast cells

  • Lab results showing overactive mast cells

Lab Tests for MCAS

  • Blood test

  • 24-hour urine studies

You should complete these labs before your first visit to a UW Health Allergy clinic. Positive lab results will help our team make a diagnosis and treatment plan.

Based on the lab results and your health history, MCAS may not be the cause of your illness. If this is the case, you and your doctor will be informed. The referral to the allergy clinic may be declined.

Your health history and symptoms will help us decide the best plan for you. We will share the care plan with your primary care doctor. Your primary doctor will be able to follow the plan and control your symptoms and any flare ups. You can make changes to this plan at follow up visits.

The low histamine diet or any other special diet plan is not backed by our doctors. These diets have not been shown to improve symptoms.

We hope you find this handout helpful. It should answer some questions you have about your symptoms and this very complex syndrome. There is a lot of information (and misinformation) about this syndrome on the internet and social media. We suggest you discuss your concerns with your doctor first before you try to diagnose yourself online.