Standardized Quantification of Mast Cells in the Gastrointestinal Tract in Adults.

Background: Current data on the normal quantity of mast cells throughout the adult gastrointestinal tract are limited in several domains. These include microanatomic localization of mast cells, standardization of staining and counting methods, and reporting of microscope field of view.

Objective: To address this lack of reliable reference ranges to facilitate the study of and diagnosis of emerging mast cell-mediated diseases.

Methods: We examined biopsies obtained from the esophagus, stomach, duodenum, and colon from an unselected cohort. Mean and peak mast cell density were determined on slides stained for tryptase and CD117, and were expressed per high power field (hpf) and surface area (mm), thus deriving reference ranges (average ± 2 SDs).

Results: For the most common hpf surface area (0.238 mm), upper limits of the derived reference ranges for average/peak mast cells were 0.15/3.67 (esophagus, tryptase), 0.70/5.98 (esophagus, CD117), 22.56/35.30 (stomach, tryptase), 31.32/53.10 (stomach, CD117), 30.28/49.77 (duodenal crypts, tryptase), 41.96/65.26 (duodenal crypts, CD117), 4.98/11.56 (duodenal villi, tryptase), 8.38/14.17 (duodenal villi, CD117), 26.58/41.08 (colon, tryptase), and 35.57/57.92 (colon, CD117). Interobserver variability was moderate to good. There was significant correlation between average and peak mast cell counts.

Conclusions: These data help standardize mast cell reference ranges throughout the gastrointestinal tract in adults, which can be used to determine whether abnormal levels of mast cells are present in patients with suspected mast cell-mediated disease. Our data show that the commonly used cutoff of 20 mast cells per hpf irrespective of the gastrointestinal tract segment is an underestimate of an appropriate cutoff in stomach, duodenum (crypt area), and colon.