How Many People Have MCAS? How to Tell If You Have It and Key MCAS Tests

Because MCAS can take up to 10 years to diagnose, Dr. Hoffman outlines the symptom patterns that suggest it and the five lab tests he considers most important, including sample handling.

Dr. Bruce HoffmanMSc, MBChB, FAARM, IFMCP · Integrative medicine educator
March 4, 2024Updated October 21, 20264 min read
A doctor runs a single thread between snapshots of a woman's life, from toddler allergies to adult flushing, while she watches her history come together as one pattern.

If you’ve been searching for solutions to your mysterious health symptoms, they could be caused by Mast Cell Activation Syndrome.

In one paragraph: a long history of inflammation-related symptoms is the main clue: childhood allergies, recurring rashes, gut problems, anxiety, headaches, insomnia, flushing, lightheadedness on standing and sensitivities to foods, chemicals and drugs. Dr. Hoffman recommends testing with a doctor experienced in MCAS, using chilled plasma histamine, 24-hour urine N-methylhistamine, plasma and urine prostaglandin D2, and chromogranin A. Because symptoms wax and wane, tests often need repeating, and positive results come back only about 20 percent of the time.

Mast cell activation syndrome (MCAS) is an immunological condition where mast cells inappropriately secrete mast cell mediators. Mediators include but are not limited to histamine, which can cause widespread and chronic inflammation.

This mediator release can be excessive and/or chronic and result in long-lasting symptoms in almost any cell of the body where their receptors are found. This can potentially affect every organ system in the body.

Some experts believe as many as 14 to 17 percent of the US population have MCAS, which is one out of every six to seven people. It’s also been estimated to take up to 10 years to reach a mast cell activation syndrome diagnosis. This is mostly due to the lack of awareness surrounding MCAS.

Because mast cell activation syndrome goes unnoticed for years, I’d like to dig a bit deeper and uncover some of the symptoms and lab work available that can help with MCAS diagnosis.

What are the symptoms of MCAS?

Patients who have MCAS typically have been struggling with inflammation-related symptoms over the years, which commonly include:

  • Having allergies as a toddler
  • Various rashes that came and went
  • Gut conditions (that may have been misdiagnosed)
  • Anxiety
  • Headaches
  • Insomnia
  • Poor wound healing

While these are common MCAS symptoms due to mast cell mediators occurring throughout the body, a person can be affected by symptoms that are more widespread. These can include, but are not limited to the following questions:

  • Feeling as though you’ve always been sick
  • Overreaction to bee stings and mosquito bites
  • Shortness of breath
  • Feeling lightheaded when you stand
  • Insomnia
  • Ringing of the ears
  • Facial and chest flushing
  • Frequent colds, infections or fevers
  • Food, chemical, and drug sensitivities and intolerances
  • Heat intolerance

You can also find a comprehensive list of MCAS symptoms in my in-depth article, Mast Cell Activation Syndrome and Histamine: When Your Immune System Runs Rampant.

You have the option to get testing done with a doctor to help confirm the MCAS diagnosis. I recommend you have these tests done with a doctor who’s experienced in MCAS because it’s still largely unknown, even in the medical community.

Which lab tests help diagnose MCAS?

Working with a doctor who specializes in MCAS is your best bet as you’ll need to get testing on multiple occasions since the symptoms of MCAS wax and wane. False negatives are a common occurrence with MCAS testing. In fact, positive lab work is only obtained 20 percent of the time. However, testing can still give you a lot of valuable information regarding your mast cell mediator status. Testing for MCAS is quite complex and requires specialized handling of tissue samples.

The most important MCAS tests are:

  • Histamine – plasma – Quest 36586 – must be chilled. Normal range – 28-51 ug/l.
  • N-Methylhistamine – 24-hour urine – must be chilled. Normal range – less than 200 mcg/g.
  • Prostaglandin D2 – plasma – must be immediately chilled and spun in a refrigerated centrifuge. Must be off NSAIDS (Motrin, Advil), aspirin, ASA, anything containing aspirin, for 5 days.
  • Prostaglandin D2 (PGD2) – 24-hour urine – specimen collection must be chilled. Must be off NSAIDS (Motrin, Advil), aspirin, ASA, anything containing aspirin, for 5 days.
  • Chromogranin A – Quest 16379 – must be off proton pump inhibitors (PPIs) and H2 blockers (Pepcid and Zantac) for 5 days before tests, since they can falsely elevate chromogranin A.

There are others you can have taken, which you can find in more detail in my in-depth article, Mast Cell Activation Syndrome and Histamine: When Your Immune System Runs Rampant.

More information regarding a low-histamine diet may found found in my guide.

Resources:

Frequently asked questions

What is mast cell activation syndrome?
MCAS is an immunological condition in which mast cells inappropriately release mediators such as histamine, which can cause widespread and chronic inflammation. Because mediator receptors are found throughout the body, it can potentially affect every organ system.
What are the symptoms of MCAS?
Common symptoms include childhood allergies, recurring rashes, gut conditions, anxiety, headaches, insomnia and poor wound healing. Wider symptoms can include shortness of breath, lightheadedness on standing, ringing in the ears, facial and chest flushing, frequent infections, heat intolerance, and food, chemical and drug sensitivities.
What lab tests are used to diagnose MCAS?
Dr. Hoffman lists plasma histamine, 24-hour urine N-methylhistamine, plasma prostaglandin D2, 24-hour urine prostaglandin D2 and chromogranin A as the most important tests. Samples require specialized handling, and most must be chilled.
Why do MCAS tests often come back negative?
MCAS symptoms wax and wane, so false negatives are common and positive lab work is obtained only 20 percent of the time. Dr. Hoffman advises testing on multiple occasions with a doctor who specializes in MCAS.
Which medications need to be stopped before MCAS testing?
NSAIDs such as Motrin and Advil, aspirin and anything containing aspirin should be stopped for 5 days before prostaglandin D2 tests. Proton pump inhibitors and H2 blockers such as Pepcid and Zantac should be stopped for 5 days before chromogranin A testing, since they can falsely elevate it.
What does Dr. Bruce Hoffman say about MCAS?
Dr. Hoffman describes MCAS as a largely unrecognized condition. He notes that some experts estimate 14 to 17 percent of the US population may have it, about one in six to seven people, and that reaching a diagnosis can take up to 10 years. He recommends testing on multiple occasions with a doctor experienced in MCAS.

More on MCAS & POTS

Everything Dr. Hoffman has written on mast cell activation syndrome, histamine and POTS: what it is, how it is tested, what triggers it and how it is treated, from the co-author of the global MCAS consensus-2 paper.

See the MCAS & POTS hub: all 13 articles →

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