A blood test could reduce the number of MRI scans for some breast cancer patients, according to a Gundersen Lutheran Medical Foundation research project.

A blood test to pinpoint the optimal timing of breast scans in women with irregular menstrual cycles likely would mean fewer repeat scans, said Dr. Richard Ellis, a Gundersen Lutheran clinical breast radiologist.

Previous studies have found that performing breast MRI scans during the follicular phase — the third to 14th days in the menstrual cycle, ending in ovulation — is the best time to get the clearest images, making it easier to help determine the size and extent of breast cancer, Ellis said.

“In practice, many clinicians scan premenopausal women who lack normal menstrual cycles, without regard to the timing of their hormonal cycle,” said Ellis, the lead author of a new study published in the December issue of the American Journal of Roentgenology.

“This can result in non-diagnostic exams and repeat scans,” he said.

The blood test used in the study determines a woman’s serum progesterone concentration, which vary predictably during the menstrual cycle.

“None of the breast MRI scans performed in our small group of women resulted in high background enhancement of normal breast tissue requiring a repeat scan,” Ellis said.

A blood test could help 5 percent to 10 percent of women with irregular menstrual cycles avoid repeat scans, he said.

“We didn’t discover anything new, but studied known information from two bodies of science — physiology and radiology — and confirmed existing science,” Ellis said. “But these two bodies have not communicated to each other what we have known, and so the science was not put into practice.”

He expects his research to result in the blood test being used more nationally. “It can save anxiety for patients,” he said, “and health care costs.”