The growing number of nurse practitioners in the United States parallels a drop in the number of registered nurses and a shift in where nurses are employed, according to a study published this week in Health Affairs

The “unprecedented” change is occurring as concerns about physician shortages have spurred rapid expansion of education programs that have attracted millennial generation workers, wrote lead author David I. Auerbach, from Montana State University’s College of Nursing.

Between 2010 and 2017, the number of NPs in the U.S. more than doubled — from about 91,000 to 190,000, according to the authors. There are also new trends in where these nurses work. Employment is now concentrated in hospitals, physician offices, and outpatient care centers, they reported.

In addition, NPs are no longer clustered in primary care but rather work across fields, said Gary LeRoy, M.D., president of the American Academy of Family Physicians, in a Medscape Medical News report. “They are in virtually every specialty of medicine,” he said.

Likewise, “[t]here are RNs who may never work in a hospital,” Brooke Trainum, JD, assistant director for policy and regulatory advocacy at the American Nurses Association, told the news outlet.

Meanwhile, the substantial growth in the number of NPs has reduced the size of the registered nurse workforce to as many as 80,000 individuals nationwide, the study’s authors found.

“In the future, hospitals must innovate and test creative ideas to replace RNs who have left their positions to become NPs, and educators must be alert for signs of falling earnings that may signal the excess production of NPs,” concluded Auerbach and colleagues.