Primary eosinophilic gastroenteritis and colitis (EGE) is a rare entity with unspecific clinical and endoscopic findings. Validated histopathologic criteria for confirming the diagnosis are lacking, because numeric values for normal or elevated concentrations of eosinophils in mucosal biopsies are varying between observers. To quantify this interobserver variance, we had the same set of 30 slides of eosinophilic-rich mucosal biopsies from the ileum and colon systematically reviewed by a panel of six independent pathologists, each with more than a ten-year experience in the field. Using a highly standardized biopsy and slide preparation protocol, we ruled out any influence by the preparation, the patient, the endoscopist, the endoscopes and calipers used, the sampling site, the fixation and staining method, and the microscopic field sizes. Still, all numeric results differed between pathologists up to a factor greater than 30. Calculated positive or negative diagnosis of EGE differed up to a factor greater than 8. A theoretical incidence for EGE calculated from these numbers differed by a factor greater than 1500. We conclude that eosinophil counts in mucosal biopsies from the lower gastrointestinal tract are subject to a very high interobserver variance. Until further research provides objective and validated methods for standardization, all epidemiologic numbers derived from histopathologic findings may have to be questioned. When diagnosing individual patients with EGE, overall morphologic picture together with clinical and endoscopic findings is more important than numeric eosinophil count.
Noninfectious, or “primary,” eosinophilic gastroenteritis/colitis (EGE / EC) is a rare entity. For clinical and practical reasons, it is distinguished from the better known eosinophilic esophagitis (EoE), although both are suspected to be caused by Th2-mediated food hypersensitivity.
Identifying patients with EGE can be demanding. Clinical symptoms like abdominal pain or recurrent diarrhea are unspecific [
Diagnosing EGE/EC therefore strongly relies on histopathologic evaluation of mucosal biopsies. But unlike in the esophagus, where diagnostic criteria for EoE are widely agreed upon [
Considering this variance, it is not surprising that there is no consensus about the threshold above which the diagnosis of “eosinophilic ileitis/colitis” can be made. Some authors suggest a value as low as at 6 eosinophils per HPF [
Because of these varying and contradictory numbers (and considering the comparatively clear situation in the esophagus), many authors suspect an undetected bias in the histopathologic findings. Possible confounders like the variability in microscopic HPF size, selection of fields near or far from lymphoid follicles, and differing criteria for including cells in the count had been discussed [
To test these hypotheses, we had the same standardized mucosal biopsies from 10 patients examined by six independent specialists in pathology who were blinded for each other’s results. Eosinophils were counted according to a standardized protocol, and results were normalized for the HPF areas of the microscopes used.
We retrospectively examined the histopathologic biopsies of 521 consecutive adult patients who underwent diagnostic ileocolonoscopy in our department from January to December 2017. 84 of them had mucosal biopsies taken because of chronic abdominal pain, recurrent diarrhea, or both. Out of these patients, 10 aroused the clinical or endoscopic suspicion of an elevated eosinophil count in the lower GIT or showed elevated eosinophils in routine histopathologic findings. These were included in the study. Excluded were all patients with inflammatory bowel disease (IBD), collagenous colitis, colonic infections, NSAID treatment, lymphoma, Meniere’s disease, and helicobacter pylori infection. All included patients were Caucasians living within < 50 Kilometers from the hospital and prepared for colonoscopy using the same macrogol-based solution (Moviprep, Norgine GmbH, Marburg, Germany).
All patients were examined by one single endoscopist (F.H.). Two biopsies were taken from 3 standardized locations each (terminal ileum, hepatic flexure, rectum) using 2.3mm calipers (MTW Wolfgang Haag KG, Germany) through flexible colonoscopes (Fujinon EC600, Fuji Corp, Japan). Probes were fixated in 4% buffered formaldehyde (R. Langenbrinck GmbH, Emmendingen, Germany) and brought to the pathologist’s laboratory. They were then embedded in 10% paraffin wax (Tissue Tek, Sakura Finetek Europe B.V., Netherlands), cut to 4
For the study, original glass slides of included patients were drawn from the archive, anonymized, and sent to the participating pathologists.
There are six clinical institutes of pathology in the state of Brandenburg. Four of them participated in the study. Mucosal biopsies were examined by six specialists in pathology with at least ten year experience in the field (Box
Microscopes used by the participating pathologists, area of their high power fields (HPF), and normalization factor [
Investigator | Microscope | Area HPF (mm2) | Normalization Factor |
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1 | Olympus Bx50 40x/0.65 | 0.237 | 1.000 |
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2 | Olympus Bx51 40x/0.75 | 0.344 | 0.699 |
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3 | Olympus Bx51 40x/0.75 | 0.344 | 0.699 |
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4 | Olympus Bx51 40x/0.75 | 0.344 | 0.699 |
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5 | Olympus Bx51 (0.55mm) 40x/0.65 | 0.237 | 1.000 |
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6 | Zeiss Axiolab 40x10/0.65 | 0.331 | 0.716 |
Director: Dr. med. Roland Pauli Hochstr. 27 14770 Brandenburg an der Havel Director: Prof. Dr. med. Stefan Koch Pieskower Straße 33 15526 Bad Saarow Director: Dr. med. Petra Besuch Müllroser Chaussee 7 15236 Frankfurt (Oder) Director: Dr. Frank Lippek Fehrbelliner Straße 38 16816 Neuruppin
Intructions for Examination: (i) The aim of this study is to count the maximum number of eosinophils per HPF in the ileal, colonic, and rectal mucosa. (ii) To do this, identify the 5 HPF with the highest number of eosinophils in every slide, then count the eosinophils in each! (iii) HPF must be located > 4 crypts from the next lymph follicle. (iv) Do (v) granula, even if their nucleus is out of focus or out of the cutting plane.
All data was analyzed using IBM SPSS Statistics 23. If not stated otherwise, eosinophilic numbers are given as mean +/- standard deviation (SD) out of 5 HPF. For metrically scaled, non-Gaussian data, Friedman test was used for more than two paired samples. Cochran Q Test was used for nominal scaled, paired samples.
Eosinophil counts in all biopsies differed between investigators, up to a factor > 30. Maximum count was 328 per HPF (mean of 5, hepatic flexure), and minimum count was 0 per HPF (mean of 5, more than one biopsy site). Analyzing each biopsy site for each patient by investigator, differences between the investigators were significant for all biopsy sites (Table
Eosinophil counts of each pathologist for each anatomic site of each patient. Values shown are mean ± SD from 5 HPF and normalized (Table
Investigator 1 | Investigator 2 | Investigator 3 | Investigator 4 | Investigator 5 | Investigator 6 | | ||||||||
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Pat | Ileum | | ±8,4 | | ±1,9 | | ±0,7 | | ±8,0 | | ±1,7 | | ±7,2 | < 0.001 |
Flexure | | ±14,2 | | ±4,1 | | ±1,1 | | ±8,2 | | ±1,2 | | ±5,5 | = 0.001 | |
Rectum | | ±6,5 | | ±1,4 | | ±0,5 | | ±1,7 | | ±1,4 | | ±3,1 | < 0.001 | |
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Pat | Ileum | | ±21,1 | | ±2,7 | | ±3,1 | | ±2,6 | | ±1,2 | | ±11,7 | = 0.001 |
Flexure | | ±1,4 | | ±6,4 | | ±1,4 | | | | ±6,3 | | ±19,6 | < 0.001 | |
Rectum | | ±12,8 | | ±1,2 | | ±4,1 | | ±14,9 | | ±0,4 | | ±18,3 | < 0.001 | |
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Pat | Ileum | | ±21,1 | | ±4,1 | | ±1,4 | | ±4,0 | | ±0,6 | | ±6,5 | < 0.001 |
Flexure | | ±9,1 | | ±1,9 | | ±2,0 | | ±7,0 | | ±1,9 | | ±3,2 | < 0.001 | |
Rectum | | ±5,6 | | ±1,9 | | ±5,2 | | ±2,1 | | ±1,2 | | ±2,9 | < 0.001 | |
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Pat | Ileum | | ±2,7 | | ±0,5 | | ±1,2 | | ±3,0 | | ±1,7 | | ±1,3 | < 0.05 |
Flexure | | ±12,8 | | ±3,0 | | ±2,0 | | ±3,6 | | ±1,6 | | ±6,0 | < 0.05 | |
Rectum | | ±2,2 | | ±0,5 | | ±0,4 | | ±2,7 | | ±0,5 | | ±1,5 | < 0.05 | |
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Pat | Ileum | | ±14,8 | | ±1,2 | | ±1,3 | | ±1,7 | | ±3,1 | | ±9,7 | = 0.001 |
Flexure | | ±13,0 | | ±1,4 | | ±1,0 | | ±2,8 | | ±2,5 | | ±1,4 | = 0.001 | |
Rectum | | ±3,2 | | ±0,9 | | ±0,8 | | ±1,4 | | ±0,9 | | ±1,1 | < 0.001 | |
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Pat | Ileum | | ±2,3 | | ±2,1 | | ±1,7 | | ±1,6 | | ±0,4 | | ±2,3 | < 0.001 |
Flexure | | ±10,0 | | ±5,2 | | ±1,7 | | ±3,7 | | ±2,3 | | ±12,6 | < 0.001 | |
Rectum | | ±0,6 | | ±1,0 | | ±0,5 | | ±1,4 | | ±0,5 | | ±1,5 | = 0.001 | |
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Pat | Ileum | | ±14,4 | | ± | | ±1,8 | | ±1,4 | | ±0,6 | | ±12,1 | = 0.001 |
Flexure | | ±1,4 | | ±3,4 | | ±1,9 | | ±2,9 | | ±1,5 | | ±6,8 | < 0.001 | |
Rectum | | ±21,1 | | ±1,7 | | ±0,9 | | ±3,9 | | ±0,6 | | ±2,5 | = 0.001 | |
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Pat | Ileum | | ±6,7 | | ±1,0 | | ±1,0 | | ±2,3 | | ±1,1 | | ±6,7 | = 0.001 |
Flexure | | ±8,7 | | ±0,6 | | ±1,5 | | ±3,2 | | ±2,0 | | ±7,4 | = 0.001 | |
Rectum | | ±3,2 | | ±1,0 | | ±0,7 | | ±2,6 | | ±0,5 | | ±1,3 | = 0.001 | |
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Pat | Ileum | | ±2,7 | | ±1,2 | | ±0,7 | | ±1,7 | | ±0,8 | | ±2,5 | < 0.001 |
Flexure | | ±8,8 | | ±1,2 | | ±1,2 | | ±2,9 | | ±0,8 | | ±6,3 | < 0.001 | |
Rectum | | ±0,6 | | ±1,3 | | ±0,5 | | ±2,1 | | ±0,5 | | ±1,0 | < 0.05 | |
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Pat | Ileum | | ±10,1 | | ±1,4 | | ±1,0 | | ±2,2 | | ±1,2 | | ±10,2 | < 0.001 |
Flexure | | ±4,6 | | ±1,6 | | ±0,7 | | ±3,4 | | ±1,7 | | ±2,6 | <0.001 | |
Rectum | | ±0,4 | | ±0,5 | | ±0,5 | | ±1,0 | | ±0,4 | | ±0,7 | < 0.05 |
Example of eosinophil counts by each investigator (from Table
Example of eosinophil counts by each investigator (from Table
Example of eosinophil counts by each investigator (from Table
Mean eosinophil counts overall differed between the highest and the lowest counting investigator by a factor of 14.5 (29 vs.2).
Intra-individually, each investigator was concordant to his own bias, i.e. the one with the highest counts overall had those highest counts in all but one biopsy, the one with the lowest count had the lowest count in all but three biopsies (Table
Independently of the strong inter interobserver observer variance, each observer found the highest number of eosinophils in the hepatic flexure, with values between 73 eosinophils per HPF for the highest counting investigator (mean of 5 HPF of all patients), and 5 for the lowest. Numbers in the ileum were intermediate in all investigators with values from 41 for the highest counting investigator, and 2 for the lowest. Numbers for the rectum were lowest with numbers from 18 for the highest counting investigator, and 1 for the lowest (Figure
Eosinophil numbers in the ileum, hepatic flexure, and rectum by different investigators (Invest. 1 to 6) examining the same 30 slides according to standardized protocol. Numbers are given as means of 5 HPF from 10 patients = 50 HPF, normalized (Table
Based on these numbers, we calculated the ratio of positive vs. negative diagnosis for “eosinophilic enterocolitis” for each pathologist, assuming a threshold of 20 eosinophils per HPF in the ileum or rectum and 50 in the hepatic flexure. Results were diverging with observer #1 diagnosing 8 (80%) positive and 2 (20%) negative, while observer #2 diagnosed 0 positive and 10 (100%) negative. Observers #3 and #5 diagnosed 1 (10%) positive and 8 (90%) negative. Observer #4 diagnosed 2 (20%) positive and 8 (80%) negative. Observer #5 diagnosed 1 (10%) positive and 9 (90%) negative, observer #6 diagnosed 3 (30%) positive and 7 (70%) negative (Figure
Positive and negative diagnoses for eosinophilic enteritis /colitis by different investigators (Invest. 1 to 6) examining the same 30 slides of 10 patients according to a standardized protocol. Thresholds were Ileum > 20 eosinophiles/HPF, hepatic flexure > 50 eosinophiles/HPF, rectum > 20 eosinophiles/HPF, normalized (Table
Extrapolating from these numbers to the 521 patients who were initially scanned for the study, we calculated a “theoretical overall incidence” for EGE / EC of 1500 per 100,000 for the highest counting investigator, and < 1 per 100,000 for the lowest counting one (Figure
Virtual incidence numbers of eosinophilic enteritis /colitis in adults calculated for each investigator based on 521 patients scanned for the study. Thresholds for positive diagnosis are > 50 Eosinophils per HPF in the hepatic flexure, and > 20 in the ileum or rectum [
Eosinophilic diseases of the lower GIT are relatively newly described, incompletely understood, rare, and difficult to detect. Clinical and endoscopic signs are non-specific; histopathologic criteria for mucosal biopsies are lacking. While all authors agree that a certain amount of eosinophils in the ileum and colon is normal, the actual numbers are not known [
Possible explanations for this discrepancy are a lack of clinicopathologic data supporting any particular threshold in the lower GIT, anatomic [
In this study, we therefore standardized the sampling, processing and examining of 30 slides from ileal, colonic and rectal biopsies from ten Caucasian patients living in the proximity of our center. We then showed the exact same glass slides to six experienced specialists in pathology and asked them to count the eosinophils according to a standardized protocol without knowing the results of each other. Results were normalized to HPF sizes. With this setup, we are confident to have ruled out any influence by the preparation, the patient, the geography, the endoscopist, the endoscopes used, the calipers, biopsy size and number, the topography of the sampling site, the staining method, and the microscopic field sizes. Still, results were strikingly differing.
When discussing this phenomenon with the participating pathologists and gastroenterologists, we did not find an explanation for it right now. One possibility is that the spotty distribution of eosinophils in the lower GIT leads to highly varying concentrations in different HPFs. The error then occurs as early as in the overview, where fields of interest are identified. So, after optical magnification of 400x, every pathologist counts five different regions of the same slide. Further studies, possibly on multiheader microscopes, may be needed to explain these discrepancies. Until then, we can only describe it as extremely high interobserver variance.
Against this background, one may have to rethink some of the facts that are thought to be known about EGE today. Overall prevalence is reported to be about 5 per 100,000 [
Since we do not know the exact reason for this phenomenon, we cannot offer a solution right now. Significantly increasing the number of biopsies and HPFs could even out the mean values, but that would be impractical in a real-life clinical situation. Another possibility could be a different staining method to identify and automatically count eosinophils in lower magnification. However, H&E staining that we used is standard for examining mucosal biopsies, and no pathologist reported problems with identifying eosinophils in the slides. So new staining and counting methods would not necessarily be suitable for daily pathologic routine but rather of scientific interest.
College of American Pathologists
Eosinophilic gastrointestinal disease(s)
Eosinophilic esophagitis
Eosinophilic gastroenteritis/colitis
Gastrointestinal tract
Hematoxylin and eosin staining
High power field
Inflammatory bowel disease
International Tumor Budding Consensus Conference
Nonsteroidal anti-inflammatory drug(s)
Standard deviation.
Original slides are archived in the Department of Pathology. Counting protocols are available from author Anna Franziska Jansen.
All authors declare that there are no conflicts of interest.
Authors Marlis Günther and Roland Pauli were taking part in the study as pathologists. The authors would like to thank the additional pathologists and institutes (see Box