A new study from Northwestern Medicine® has found that surgical researchers rarely use female animals or female cells in their published studies, despite a huge body of evidence showing that sex differences can play a crucial role in medical research.


Editors of the five major surgical journals reviewed in this study have responded to this finding and will now require authors to state the sex of animals and cells used in their studies. If they use only one sex in their studies, they will be asked to justify why.

“Women make up half the population, but in surgical literature, 80 percent of the studies only use males,” said Melina R. Kibbe, MD, senior author of the study and a vascular surgeon at Northwestern Medicine®.

“We need to do better and provide basic research on both sexes to ultimately improve treatments for male and female patients.”

Published Aug. 28 in the journal Surgery, the study follows a 60 Minutes segment in February about the problem of overlooking sex differences in biomedical research, featuring Northwestern Medicine® scientists Teresa Woodruff and Kibbe.

Following the “60 Minutes” piece, the National Institutes of Health announced that they are developing a policy that will require all of its funded researchers to study both sexes for all pre-clinical research (the animal and cell studies performed before human studies).

Basic science research has shown repeatedly that male and female animals metabolize drugs differently. Accordingly, the research shows that men and women may experience differences in the ways they manifest diseases, experience illnesses and benefit from treatments.

“Requiring the sex of animals and cells is a very small thing to ask of authors,” Kibbe said. “It should be a requirement of all medical journals.”

Kibbe is a member of the Women’s Health Research Institute and is the Edward G. Elcock Professor of Surgical Research at Northwestern University Feinberg School of Medicine.

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