How to Get Diagnosed with MCAS: Tests, Criteria, & Doctor Questions

Mast Cell Activation Syndrome (MCAS) is a complex and often misunderstood condition that can significantly impact a person's quality of life. Characterized by the inappropriate release of chemical mediators from mast cells, MCAS can lead to a wide range of symptoms affecting multiple body systems. Navigating the diagnostic process can be challenging, but understanding the criteria, key tests, and what to discuss with your healthcare provider can empower you on your journey to diagnosis and effective management. For more, see our what MCAS is.

Understanding Mast Cell Activation Syndrome (MCAS)

Mast cells are a crucial part of your immune system, acting as first responders to perceived threats like allergens or pathogens. When activated, they release various chemical mediators, including histamine, prostaglandins, and leukotrienes, which trigger inflammatory responses. In individuals with MCAS, these mast cells become overly sensitive and release mediators inappropriately, even without a clear external trigger [1]. This leads to a cascade of symptoms that can vary widely in severity and presentation.

Symptoms of MCAS can affect nearly every organ system in the body. Common manifestations include skin issues (flushing, hives, itching, swelling), gastrointestinal problems (abdominal pain, diarrhea, constipation, nausea, vomiting), cardiovascular symptoms (low blood pressure, rapid heart rate), respiratory issues (shortness of breath, nasal congestion), and neurological symptoms (headaches, brain fog, fatigue). To be considered MCAS, symptoms typically affect two or more body systems [2].

The Challenges of Diagnosing MCAS

Diagnosing MCAS can be a lengthy and frustrating process, often taking years from symptom onset. This diagnostic delay stems from several factors:

• Widespread and Varied Symptoms: The diverse and often seemingly unrelated symptoms of MCAS can mimic many other conditions, making it difficult for healthcare providers to connect them to a single underlying cause [2].
• Lack of Specific Biomarkers: There isn't a single definitive test for MCAS. Diagnosis relies on a combination of clinical presentation, laboratory findings, and response to treatment [2].
• Episodic Nature of Symptoms: MCAS symptoms often occur in flares, which can make it challenging to capture elevated mediator levels during testing if the patient is not actively experiencing an episode [2].
• Limited Awareness: Despite growing recognition, many healthcare providers may not be familiar with MCAS, leading to misdiagnosis or delayed diagnosis [3].

Diagnostic Criteria for MCAS

The diagnosis of MCAS typically follows a set of consensus criteria, with the Molderings/Afrin consensus criteria being widely recognized. While specific wording may vary slightly between different guidelines, the core components generally include:

Major Criteria

1. Presence of typical clinical symptoms: Patients must experience recurrent, systemic symptoms indicative of mast cell activation, often affecting two or more organ systems. These symptoms can include anaphylaxis, flushing, itching, hives, abdominal pain, diarrhea, nausea, vomiting, shortness of breath, and cardiovascular issues [2].

Minor Criteria

1. Evidence of increased mast cell mediators: This involves laboratory tests showing an elevation in mast cell mediators (or their metabolites) during symptomatic periods compared to baseline levels. The most commonly assessed mediators include serum tryptase, 24-hour urine N-methylhistamine, 24-hour urine prostaglandin D2 (PGD2), and 24-hour urine 11β-prostaglandin F2α [3].
2. Response to mast cell-targeted therapy: A significant improvement in symptoms with the use of medications that stabilize mast cells or block the effects of mast cell mediators (e.g., antihistamines, mast cell stabilizers) supports the diagnosis [2].

It's important to note that a diagnosis of MCAS requires meeting the major clinical criteria and at least one of the minor criteria. The interpretation of these criteria often requires clinical expertise due to the nuances of symptom presentation and test results.

Key Diagnostic Tests for MCAS

Several laboratory tests are used to support an MCAS diagnosis. These tests aim to detect elevated levels of mast cell mediators or their breakdown products, particularly during symptomatic flares.

Serum Tryptase

Serum tryptase is a key biomarker for mast cell activation. It is an enzyme released by mast cells, and elevated levels can indicate mast cell degranulation. For MCAS diagnosis, it's crucial to measure tryptase levels during a symptomatic episode (acute) and compare them to a baseline level (when symptoms are minimal or absent). A significant increase (e.g., a 20% increase plus 2 ng/mL over baseline) is often considered supportive evidence [3]. However, normal tryptase levels do not rule out MCAS, as some individuals with the condition may not have elevated tryptase [2].

24-Hour Urine Mediators

Measuring mast cell mediators in a 24-hour urine collection can provide a more comprehensive picture of mast cell activity, as mediator levels can fluctuate rapidly in the blood. Key urine tests include:

• 24-hour urine N-methylhistamine: Histamine is a primary mediator released by mast cells. Elevated levels in urine can indicate increased mast cell activity.
• 24-hour urine prostaglandin D2 (PGD2) and 11β-prostaglandin F2α: Prostaglandins are another class of mediators released by mast cells. Elevated levels of their metabolites in urine are strong indicators of mast cell activation [3].

These urine tests are often more sensitive than serum tryptase for detecting MCAS, especially in cases where tryptase levels remain normal [3]. Collecting these samples during a flare is ideal, but random urine samples can also be useful due to the increased stability of mediators in urine [3].

Other Tests to Consider

While not primary diagnostic tests for MCAS, other investigations may be conducted to rule out other conditions or assess for comorbidities:

• Complete Blood Count (CBC) with differential: To check for other blood disorders.
• Immunoglobulin levels: To assess immune function.
• Allergy testing (skin prick or blood tests): To rule out traditional allergic reactions as the sole cause of symptoms [2].
• Bone marrow biopsy: In some cases, particularly if systemic mastocytosis (a more severe mast cell disorder) is suspected, a bone marrow biopsy may be performed to look for abnormal mast cell accumulation or morphology.

Which Specialists to See

Given the complexity of MCAS, a multidisciplinary approach is often beneficial. The following specialists may be involved in the diagnostic and management process:

• Allergist/Immunologist: These specialists are often the primary physicians involved in diagnosing and managing MCAS, as they have expertise in mast cell disorders and allergic conditions [2].
• Gastroenterologist: For patients experiencing significant gastrointestinal symptoms.
• Neurologist: For those with prominent neurological manifestations like headaches, brain fog, or neuropathic pain.
• Dermatologist: For persistent skin issues such as chronic hives or flushing.
• Cardiologist: If cardiovascular symptoms like POTS (Postural Orthostatic Tachycardia Syndrome) are present.
• Geneticist: In some cases, to investigate potential underlying genetic predispositions.

Finding a healthcare provider who is knowledgeable about MCAS is crucial. Patient advocacy groups and online communities can sometimes provide recommendations for specialists in your area.

What to Ask Your Doctor

Preparing a list of questions to bring to your appointment can help ensure you get the most out of your consultation. Here are some questions to consider asking your doctor:

Key Takeaways

• MCAS is a complex condition involving inappropriate mast cell activation, leading to diverse symptoms across multiple body systems.
• Diagnosis is challenging due to varied symptoms, lack of a single definitive test, and episodic flares.
• The Molderings/Afrin consensus criteria guide diagnosis, requiring clinical symptoms, evidence of elevated mast cell mediators, and response to treatment.
• Key diagnostic tests include serum tryptase and 24-hour urine tests for N-methylhistamine, PGD2, and 11β-prostaglandin F2α.
• A multidisciplinary team, often led by an allergist/immunologist, is beneficial for diagnosis and management.
• Prepare a list of questions for your doctor to discuss symptoms, diagnostic steps, treatment options, and long-term management.

References

[1] Cleveland Clinic. (2024). Mast Cell Activation Syndrome (MCAS): Symptoms & Treatment. Retrieved from https://my.clevelandclinic.org/health/diseases/mast-cell-activation-syndrome [2] Mayo Clinic Laboratories. (n.d.). Mast cell activation syndrome - Insights. Retrieved from https://news.mayocliniclabs.com/immunology/mast-cell-activation-syndrome/ [3] Afrin, L. B., Molderings, G. J., et al. (2020). Diagnosis of mast cell activation syndrome: a global “consensus-2”. Retrieved from https://www.mastcellaction.org/assets/_/2021/05/26/3fe9e463-1058-4c0f-863a-f2524839949d/2020-afrin-diagnosis-of-mast-cell-activation-syndrome-a-global-consensus-2-final.pdf?v=1