BREESI & QUEESI: Tips for Diagnosing MCAS

Mast cell activation syndrome (MCAS) is inherently complex, and it can manifest in a bewildering number of ways. Patients may experience waxing and waning symptoms in seemingly unrelated organ systems, with no obvious pattern.

MCAS overlaps with other chronic syndromes such as Ehlers-Danlos (EDS), Postural Orthostatic Tachycardia Syndrome (POTS), and chronic fatigue/fibromyalgia.

It’s a complicated picture, but there are a few tools and tip-offs that can help you make sense of what’s going on, says Tania Tyles Dempsey, MD, a physician who specializes in diagnosing and treating MCAS.

MCAS patients may have hypermobile joints, a common finding in those who also have EDS. Many have histories of cysts, thyroid nodules, benign tumors, or other aberrant growths. MCAS typically has its onset before age 20, and many patients struggle for years if not decades before finding help.

Three Simple Questions

Since most MCAS patients also have chemical and food sensitivities, the Brief Environmental Exposure and Sensitivity Inventory (BREESI) is a quick way to get a lot of helpful information. BREESI is a research-validated clinical tool consisting of these three simple questions:

Do you feel sick (headache, brain fog, weakness, dizziness, shortness of breath, stomach upset) when exposed to tobacco smoke, cleaning supplies, nail polish, gasoline, fresh tar, asphalt, new carpets, furnishings, air “fresheners,” pesticides, etc?

Are you unable to tolerate or have you had adverse reactions to antibiotics, pain killers, anesthetics, contrast dyes, oral contraceptives, vaccines, or medical prostheses and other such devices?

Are you unable to tolerate or do you react to dairy, corn, wheat, eggs, soy alcohol, caffeine, food additives (MSG, food dyes)?

Claudia S. Miller, MD

BREESI is a bare-bones version of the Quick Environmental Exposure and Sensitivity Inventory (QEESI), an extensive 50-question tool developed by Claudia Miller, MD, at the University of Texas School of Medicine, San Antonio.

Though not definitively diagnostic for MCAS, a “yes” answer on the three BREESI questions should raise your index of suspicion. These patients may benefit from a deeper assessment using QEESI.

Extreme chemical sensitivity, which is very common among MCAS patients, is indicative of Toxicant-Induced Loss of Tolerance (TILT), says Dr. Dempsey.

What happens is exposure to a particular trigger—it could be exposure to mold, heavy metals, volatile toxins, certain medications, tick bite, or infections like Covid—causes a rapid loss of tolerance to environmental stressors, especially chemical stressors. People are suddenly far more sensitive than they were previously. Low levels of toxins that were formerly tolerable will now trigger cascades of symptoms.

Lab & Genetic Signs of MCAS:

  • Histamine elevations: Plasma histamine levels greater than 8nmol/L are highly suggestive of MCAS.
  • Tryptase elevations: All mast cells can produce tryptase. Plasma tryptase elevations were once considered a hallmark of MCAS. This sign is highly suggestive, but it is also variable. Not all MCAS patients show tryptase elevations, and mast cells also produce many other mediators.
  • Hereditary Alpha tryptasemia (HAT): This is a genetic polymorphism that predisposes to excess tryptase production. People with this trait often have MCAS, though absence of HAT does not rule out MCAS.
  • Heparin elevations: According to Dr. Dempsey, elevated plasma heparin in the absence of any other obvious cause, is highly specific for MCAS. This is common in women who have dysfunctional uterine bleeding, unusually heavy periods, or similar issues.
  • Random and 24-hour urine tests: Elevations in urinary N-methyl histamine, prostaglandin D2, 11-b-prostaglandin F2, and a-leukotriene are all strongly suggestive of MCAS in patients with characteristic symptoms.
  • Biopsy: Though definitely not a routine diagnostic method, tissue biopsies—especially from the GI mucosa—can provide a lot of data. CD117-staining of GI epithelium will reveal mast cells. A count of greater than 20 per high-power (40x) field is a strong indicator of MCAS.


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