Seasonal variation of eosinophil counts in histologically normal colonic mucosal biopsies.

Introduction: The eosinophil counts in colonic biopsies are affected by geographical and possibly seasonal variations. This study aims to investigate the significance of seasonal variations of eosinophil counts in histologically normal colonic mucosal biopsies.

Materials and methods: This is a retrospective, cross sectional study that included 337 cases of normal colonic biopsies. The number of eosinophils per high power field was counted in the most densely populated area. The eosinophilic counts were compared among genders, age groups, biopsy sites and in various months and seasons. Two tailed T-test was used to compare means and a p value < 0.05 was considered significant.

Results: 173 (51%) of cases were from males. The age range was between 18-82 with the mean being 51.7 years (SD= 17.5). 181 (54%) biopsies were from the right colon and 156 (46%) from the left colon. There was a statistically significant difference between eosinophil counts in the right colon (mean 20.2, SD 13.2) and left colon (mean 13.8, SD10.1); p value <0.001. The mean eosinophil counts was highest in autumn (21.1) followed by spring (18.3). The counts in winter and summer were close (15.2 and 15.1 respectively). There was a statistically significant difference between counts in autumn and summer (p=0.013) and between autumn and winter (p=0.008). However, there was no statistically significant differences between autumn and spring counts (p=0.183). When stratified according to site, this pattern of statistical significance was observed in the right colon but not the left colonic mucosal biopsies.

Conclusion: There are significant seasonal variations of eosinophil counts in normal colonic biopsies which are more pronounced in the right colon. Pathologists and gastroenterologists need to be aware of these variations and to take them into account when determining if a patient has tissue eosinophilia.