Can You Test for Mast Cell Activation Syndrome (MCAS)?
- 8 hours ago
- 6 min read
One of the most common questions we receive at The Autoimmune Clinic is:
"Can I be tested for MCAS?"
Every week, we hear from people looking for MCAS testing or hoping to finally receive a diagnosis of Mast Cell Activation Syndrome (MCAS).
The answer is that yes, testing for MCAS is available. However, it's important to understand that MCAS testing is more complex than most people realise. Unlike many other conditions, there is no single blood test that can reliably confirm or rule out MCAS.
Understanding why can save you both frustration and unnecessary expense, and instead focus on taking actionable step to reduce symptoms.
What Are Mast Cells?
Before explaining more about MCAS testing, it helps to understand what mast cells actually are.
Mast cells are specialised immune cells that help protect us from infection, injury and environmental threats. They are perhaps best known for their role in allergies, but they also play important roles in immune regulation, wound healing, blood vessel function and communication with the nervous system.
Unlike many immune cells, mast cells don't spend much time circulating in the bloodstream. Instead, they live within our tissues, particularly in areas that are constantly exposed to the outside world, including:
Skin
Gastrointestinal tract
Airways and lungs
Nose and sinuses
Around blood vessels
Around nerves
Bladder and reproductive tissues
This allows them to respond quickly whenever they detect something they perceive as a threat.
What Do Mast Cells Release?
When activated, mast cells release hundreds of chemical messengers known as mediators.
Some of the most important include:
Histamine
Tryptase
Prostaglandin D₂
Leukotrienes
Platelet-Activating Factor (PAF)
Heparin
Cytokines (including TNF-α and IL-6)
Chemokines
Vascular Endothelial Growth Factor (VEGF)
Each mediator affects different tissues throughout the body, which explains why MCAS symptoms can vary so widely between individuals.
MCAS Symptoms: When Should You Consider Mast Cell Activation Syndrome?
Because mast cells exist throughout the body, MCAS symptoms can involve multiple organ systems.
Common symptoms include:
Skin
Flushing
Itching
Hives
Swelling
Dermatographia
Digestive System
Bloating
Abdominal pain
Diarrhoea
Nausea
Acid reflux
Food reactions
Respiratory System
Wheezing
Shortness of breath
Nasal congestion
Throat tightness
Cardiovascular System
Palpitations
Feeling faint
Dizziness
Low blood pressure
Nervous System
Brain fog
Headaches
Anxiety
Light sensitivity
Fatigue
One important feature of Mast Cell Activation Syndrome is that symptoms affect at least two different body systems.
For example, someone experiencing flushing alongside digestive symptoms, or hives together with dizziness and palpitations, raises more suspicion of MCAS than someone with symptoms confined to a single system.
If someone only has eczema, only asthma or only IBS, we are generally less suspicious that MCAS is the primary explanation, although every case is individual.
MCAS and Allergies: They're Not Always the Same Thing
Many people assume MCAS simply means having allergies. In reality, it's more complicated than that.
In classic allergies, mast cells are activated through IgE antibodies. This is known as IgE-mediated mast cell activation.
When someone with a peanut allergy eats peanuts, for example, IgE antibodies trigger mast cells to release histamine and many other inflammatory mediators.
However, mast cells can also become activated without IgE.
Common non-allergic triggers include:
Temperature changes
Stress
Hormonal fluctuations
Certain medications
Physical pressure or friction
Environmental chemicals
Some foods and food additives
Many people experience both allergic and non-allergic mast cell activation, making diagnosis even more complex.
Why MCAS Testing Can Be Difficult
This is where many people become frustrated.
Mast cells live in tissues
One of the biggest challenges with MCAS testing is that mast cells are tissue-based cells.
If mast cell activation is occurring mainly in the gut, skin or lungs, the mediators released may never appear in significant amounts within the bloodstream.
In other words, the reaction may be very real, but a blood test may not capture it.
Many mast cell mediators are short-lived
Another challenge is that several mast cell mediators disappear very quickly.
Histamine, for example, has a very short half-life.
This means that MCAS testing is often most helpful when performed during, or very shortly after, a flare. Unfortunately, symptoms don't usually occur conveniently during laboratory opening hours.
Many MCAS markers are not specific to mast cells
Another important limitation of MCAS testing is that not every marker measured comes exclusively from mast cells.
Markers such as TNF-α, IL-6 and VEGF can also be produced by many other immune cells during inflammation or infection.
Even tryptase, which is one of the more mast cell-specific markers, has its limitations. While persistently elevated tryptase is more suggestive of conditions such as systemic mastocytosis, many people with MCAS have a normal baseline tryptase level. Some may experience only a temporary rise during an acute flare, while others may not show a measurable increase at all.
An abnormal result therefore doesn't automatically confirm MCAS, while a normal result certainly doesn't exclude it.
There is no single definitive MCAS test
Despite advances in our understanding of mast cell biology, there is currently no single laboratory test that definitively diagnoses MCAS.
Instead, diagnosis is based on combining:
Clinical history
Symptom pattern
Symptoms affecting multiple organ systems
Response to treatment
Excluding alternative diagnoses
Laboratory findings where appropriate
So How Do We Approach MCAS Testing in Clinic?
Although we do have access to MCAS testing and specialist laboratory investigations, in day-to-day clinical practice we rarely rely on laboratory results.
Instead, we spend considerable time understanding your story.
We explore:
When symptoms first appeared
Whether symptoms fluctuate or occur in flares
Which body systems are involved
Potential triggers
Previous infections
Environmental exposures
Stress and nervous system health
Previous treatments and what has or hasn't helped
Often one of the biggest clues comes from something very simple.
A client may tell us:
"I felt better while taking antihistamines, but I don't want to rely on them every day."
Information like this can often provide valuable insight alongside laboratory testing.
Why Response to Treatment Often Matters More Than MCAS Testing
One of the recognised features of MCAS is that symptoms often improve when mast cell mediators are successfully reduced or blocked.
For this reason, we tend to use a carefully monitored therapeutic approach.
Depending on the individual, this may include:
Nutraceuticals that help stabilise mast cells
Supporting histamine breakdown and clearance
Optimising nutrients involved in histamine metabolism
Supporting diamine oxidase (DAO) activity where appropriate
A lower-histamine diet
Temporary low-FODMAP intake reduction when gut inflammation seems to be contributing
Nervous system support to encourage a healthier balance between stress and rest-and-digest physiology
One important point to make: mast cells release far more than histamine.
Although histamine is often a major contributor to symptoms, mast cells can also release tryptase, prostaglandins, leukotrienes, cytokines, platelet-activating factor (PAF), heparin and many other inflammatory mediators. The exact combination of mediators released can vary from one person to another and even from one flare to the next.
This helps explain why two people with MCAS can experience very different symptoms. It also explains why antihistamines alone don't always provide complete relief. Whilst they can be very effective at blocking the effects of histamine, they do not block many of the other mediators that mast cells release.
This is one of the reasons why we often take a broader approach to support, looking not only at blocking histamine, but also at stabilising mast cells, identifying and removing triggers, addressing gut health where appropriate, and regulating the nervous system. The aim is to reduce mast cell activation itself, rather than just blocking one of the many chemicals they release.
What Happens If Initial MCAS Support Doesn't Work?
A lack of response doesn't necessarily mean mast cells aren't involved.
If symptoms remain highly suggestive of MCAS, we may work alongside an independent prescriber to explore prescription options such as:
H1 antihistamines
H2 antihistamines
Mast cell stabilisers
Leukotriene receptor antagonists
Other immune-modulating medications where clinically appropriate
Should You Invest in MCAS Testing?
If you're considering MCAS testing, it's worth discussing your case with a practitioner before spending money on specialist laboratory investigations.
Testing can have its place and, in some cases, can provide valuable supporting evidence. However, it's important to understand that MCAS testing is rarely a simple yes-or-no answer.
A normal test does not necessarily mean you don't have mast cell activation, and an abnormal result doesn't automatically prove that mast cells are responsible for your symptoms.
At The Autoimmune Clinic, we aim to help you decide where your money is best spent. Sometimes that means arranging MCAS testing, but often, it means using a detailed clinical assessment and carefully targeted interventions that provide far more useful information than laboratory results alone.
Often, symptoms speak loud enough for themselves. Our goal is not just to find abnormal test results, it's to understand what's driving your symptoms and develop a personalised plan that helps you feel better.
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At The Autoimmune Clinic, we specialise in supporting people living with complex chronic illnesses, including autoimmune diseases, Mast Cell Activation Syndrome (MCAS), chronic fatigue syndrome (ME/CFS), Long COVID, mould-related illness (CIRS), autoimmune disease and persistent digestive disorders.
Our approach combines evidence-informed functional medicine with personalised care, helping you understand the underlying drivers of your symptoms and develop a support plan tailored to your individual needs.
