IIB or not IIB, part 1: retrospective evaluation of Kenney–Doig categorization of equine endometrial biopsies at a veterinary diagnostic laboratory and comparison with published reports

Abstract

The Kenney–Doig scale is a histopathology categorization (grading) system often used as the standard for assessing endometrial disease and communicating prognostic fertility information for equine breeding prospects. We investigated how Kenney–Doig categories compared within the same institution and across different institutions to determine if observer variability may contribute to category frequencies. We conducted a retrospective analysis of all equine endometrial submission records between 1998 and 2018 at the Western College of Veterinary Medicine (WCVM) and Prairie Diagnostic Services (PDS). Of 726 biopsies, we found the following category distribution: 46 of 726 (6.3%) I, 307 of 726 (42.3%) IIA, 326 of 726 (44.9%) IIB, and 47 of 726 (6.5%) III. We also conducted a review of the literature and included 6 studies reporting Kenney–Doig category distributions. Chi-square analysis showed significant differences between the category distribution found at WCVM and PDS and the category distribution reported in the 6 studies. To account for differences in mare populations, individual category distributions were generated for 5 pathologists at the WCVM and PDS. The Fisher exact test among these 5 Kenney–Doig categories revealed significant differences in category tendencies, suggesting that observer variation affects the use of the scale. Our results suggest that there is a need for prospective inter-rater and intra-rater agreement studies of the repeatability of the Kenney–Doig scale.

Assessment of Connective Tissue in the Equine Uterus and Cervix: Review of Clinical Impact and Staining Options

“…Infertility is considered a major health problem in mares, as horses, among other domestic animals, have the lowest fertility rates, which is associated with their longevity and usage [ 1 , 2 , 3 ]. Age-related uterine diseases, such as endometritis, endometrosis, glandular differentiation disorders, and angiosis [ 3 , 4 , 5 , 6 ], are especially important, as improved management and care elongate lifespan, and many mares are bred only after successful sport or racing career [ 1 , 2 ]. Thus, especially in horses, a thorough and reliable diagnosis regarding fertility prognosis seems to be an important issue affecting the profitability of horse breeding.…”

“…Thus, especially in horses, a thorough and reliable diagnosis regarding fertility prognosis seems to be an important issue affecting the profitability of horse breeding. Sub- or infertility is causing economic losses in the equine industry and hampering efficient and effective breeding, as well as genotypic improvements among breeds [ 1 , 7 ].…”

The problem broodmare—Looking beyond the endometrial swab

“…Uterine biopsy is a well‐described technique with a standardised grading system available which can be helpful in prognosticating the mare's future reproductive potential and understanding the degree of inflammation and fibrosis involved (Westendorf et al, 2022).…”

IIB or not IIB, part 2: assessing inter-rater and intra-rater repeatability of the Kenney–Doig scale in equine endometrial biopsy evaluation

“…5 A 4×4 table was selected for the 4 possible Kenney-Doig categories available, the power set at 90% with an alpha level of 0.05, and the K1 and K2 values selected at 0 and 0.4, respectively. This resulted in a suggested minimum sample size of n = 25; however, given the unequal frequency distributions observed in our previous retrospective study 54 and the possibility that participating pathologists would categorize in similar distributions, we doubled this number for a minimum sample size of n = 50. 5 Weighted kappa values were not taken into account for sample size given that weighted kappa statistics are more sensitive at measuring agreement than unweighted and therefore require smaller sample sizes in general.…”

“…Our previous work involving retrospective evaluation of the Kenney–Doig grading distribution of biopsies submitted to the Western College of Veterinary Medicine (WCVM; University of Saskatchewan, Saskatoon, Saskatchewan, Canada) and Prairie Diagnostic Services (PDS; Saskatoon, Saskatchewan, Canada) revealed a non-uniform spread of categories with a high incidence of biopsies assigned within the 2 middle categories, IIA and IIB. 54 Although the effect of mare population dynamics on category distribution cannot be excluded, observer variation may also contribute to the significantly higher incidence of middle-ranked categories, as has been seen in other histopathology grading systems in veterinary medicine. 19,35 Examination of the individual grading tendencies of 5 of the contributing pathologists at the WCVM and PDS revealed significant differences in category proportions, suggesting that observer bias and possible disagreement regarding use of the scale may be occurring.…”