Mast cellMast cell A type of white blood cell produced in the bone marrow. They help defend against infections and play a key role in allergic reactions. In SM, mast cells become overactive and build up throughout the body. counts from gastrointestinal (GI) biopsies and the tryptaseTryptase A protein enzyme that is primarily produced by mast cells and stored in small pockets within the cells, known as granules. High levels of tryptase are a key indicator of SM. depletion index (TDI) — a marker of mast cell activationMast cell activation Describes when mast cells release histamine and other mediators into the blood stream in response to an allergen or other trigger. This leads to symptoms like fatigue, rash and, in severe cases, anaphylaxis. — showed limited ability to distinguish systemic mastocytosis (SM) from other diseases with elevated mast cell counts, found a study recently published in Archives of Pathology & Laboratory Medicine.
To determine if increased mast cell numbers in GI biopsies could help when diagnosing mast cell activation syndrome (MCAS), SM other conditions affecting the GI tract, the researchers analyzed GI biopsy samples from 128 patients at a European mastocytosisMastocytosis Rare disease caused by the buildup of mast cells. Cutaneous mastocytosis primarily affects the skin and is more common in children, while systemic mastocytosis affects internal organs and is more common in adults. reference center: 54 with MCAS, 10 with SM, 26 with other inflammatory conditions and 38 healthy controls. The researchers also evaluated the TDI to determine if mast cells were actively releasing inflammatory substances.
The study found substantial overlap in mast cell counts across groups, limiting their diagnostic value. In the upper GI tract, median counts were higher in healthy controls than in patients with MCAS (an average of 45.5 versus 42). Patients with SM had an average mast cell count of 54, but individual patients ranged from 20 to 98. In the lower GI tract, average counts were slightly higher in the MCAS group (45) and SM group (63) than in healthy controls (35.5), but again these differences were inconsistent.
TDI levels were also similar across all groups, suggesting that differences were driven by measurement variability rather than true mast cell activation and did not improve diagnostic differentiation.
“Our findings suggest that mast cell quantification in GI biopsies has limited diagnostic utility in distinguishing MCAS from other conditions or healthy controls,” the authors wrote.
The study also noted that natural variation across different segments of the GI tract may create the false appearance of increased mast cell counts.
Read more about SM testing and diagnosis
While mast cell density alone is not sufficient for diagnosis, biopsies remain important for identifying SM. In these cases, pathologists rely on specific markers, such as KIT genetic mutations and the presence of CD25 or CD30 on the cell surface, which are not seen in healthy controls or most other conditions.
The research team suggested that pathologists and clinicians should be cautious when interpreting GI biopsy reports that mention high mast cell counts in isolation.
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