MCAS Diagnosis
Mast Cell Activation Syndrome: Diagnosis
MCAS diagnosis can be challenging because its symptoms often overlap with other conditions. It is a clinical diagnosis, based on a person’s symptoms, medical history, response to treatment, and test results.
Since mast cells affect many body systems, people with MCAS often see several specialists — immunologists, allergists, gastroenterologists, or neurologists — before finding answers. Some doctors may also run genetic or bone marrow tests if they suspect mastocytosis, a more serious mast cell disease.
While the diagnostic process can feel overwhelming, receiving an accurate mast cell activation syndrome diagnosis is often a relief. It gives a name to the chaos and opens the door to targeted treatments — whether that’s antihistamines, dietary adjustments, or lifestyle changes that reduce triggers.
Key Steps in Diagnosing MCAS
Getting a mast cell activation syndrome (MCAS) diagnosis can take time, and for many people, it comes only after years of unexplained symptoms. MCAS happens when immune cells called mast cells release too many chemicals — like histamine or tryptase — at the wrong times.
Because these symptoms come and go and don’t fit neatly into one medical category, getting an MCAS diagnosis often starts with pattern recognition. Doctors look for recurring episodes that affect at least two body systems. For example, the skin and digestion.
People often notice flares after certain triggers such as heat, stress, food, or fragrances. So, keeping a symptom diary can help connect those dots and give doctors a clearer picture of what’s going on.
Testing Mast Cell Activity
There are formal criteria used to confirm a mast cell activation syndrome diagnosis. Typically, doctors look for three things:
While no single test can confirm a MCAS diagnosis, there are tests that focus on measuring chemical mediators released by mast cells, especially during a flare. Common tests include blood or urine measurements of tryptase, histamine, prostaglandin D2, leukotriene C4 and other mast cell mediators.
Since these markers can fluctuate, tests are often done when symptoms are active to improve accuracy. But, it’s important to note that even a negative test does not rule out mast cell activation syndrome.
Note: The information presented on this page has been reviewed and approved by a member of our Medical Leadership Board.
Take the first step towards understanding tick-borne disease with an exclusive guide to something here, all backed by world-leading science.
Could your symptoms be due to a tick-borne disease infection?
