MCAS Diagnosis

TLDR - MCAS is incredibly subjective and difficult to diagnose.

Symptoms

The list of MCAS symptoms is endless, spanning multiple biological systems. Your body (or specific parts of it) perceives harmless substances from your environment or diet as threats. This danger reaction can occur in many different locations, leading to various disruptions in biological processes. This is why the range of symptoms is so large. In short, homeostasis is disrupted because your body is in a state of perceived danger. Note that many of these overlap with CIRS symptoms.

• Skin Symptoms:

  • Itchy skin

  • Rashes or hives

  • Flushing (hot, red, or pink skin)

  • Swelling (angioedema), often of the face, lips, eyes, tongue, or throat)

• Gastrointestinal Symptoms:

  • Nausea

  • Vomiting

  • Diarrhea (sometimes alternating with constipation)

  • Abdominal (belly) pain

  • Bloating

• Cardiovascular Symptoms:

  • Low blood pressure

  • Rapid or irregular heartbeat

  • Dizziness or fainting

• Respiratory Symptoms:

  • Shortness of breath

  • Wheezing

  • Nasal congestion

• Neurological Symptoms:

  • Memory loss or trouble thinking (brain fog)

  • Headaches

  • Numbness or tingling

• Musculoskeletal Symptoms:

  • Joint pain

  • Muscle pain

  • Weakness

• Systemic Symptoms:

  • Anaphylaxis (severe allergic reaction involving multiple symptoms)

  • Fatigue

  • General malaise

Diagnosis

• Testing: There aren’t great clear cut tests for MCAS. Below are a few options:

  • Tryptase Levels: Measuring serum tryptase levels, which are typically elevated during an acute mast cell activation event. This is the most common way to diagnose MCAS.

  • Histamine Levels: Checking for elevated plasma or urine histamine levels.

  • N-Methylhistamine: A metabolite of histamine, often measured in a 24 hour urine sample.

  • Note that many people test negative but still believe they have MCAS. In my opinion, MCAS occurs when the body is in a heightened danger response to various environmental factors. Allergists only test for specific responses, leaving many possibilities untested.

• Response to Treatment: If symptoms improve with treatments targeting mast cell mediators, this supports an MCAS diagnosis. This includes H1 and H2 antihistamines and mast cell stabilizers like cromolyn sodium, and leukotriene inhibitors​.

• Ruling Out Other Diagnoses: It's also important to rule out any other potential conditions that could cause similar symptoms to MCAS​.