Is an endometrial swab the best screening tool for endometritis, or inflammation of the uterine lining (endometrium)? Not according to a recently published study from Denmark in Theriogenology that compared endometrial swabs with biopsies to determine which method was more reliable for diagnosis.

“We want to be able to diagnose mares with endometritis,” says Jesper Nielsen, DVM, who conducted the study, “because when left untreated, endometritis results in barren mares.” Bacterial culture of the endometrium using a swab sample is a practical, non-invasive way to screen for endometritis, and using swabs for culture is common practice. But false negative results can occur, particularly in mares with fluid in the uterus.

“We believed we would be able to diagnose more mares if we cultured biopsy samples instead of swabs,” Nielsen explained. A biopsy sample isn’t simply submitted for culture. It is also examined for signs of inflammation–the hallmark of endometritis.

Over 200 mares were examined for Nielsen’s study prior to being bred. An endometrial biopsy was collected first, followed by a swab of the endometrium. Both samples were prepared for bacterial culture, but the biopsy was also examined for cellular evidence of inflammation. When the two methods were compared statistically, both were found to be very accurate for positive culture results–false positives were not a problem. However, when the results were negative, the endometrial biopsy was more reliable–it had 41% fewer false negatives