Up to one-quarter of hospital patients are returning to emergency rooms within a month of their discharge, a new study by Penn researchers has found.

The ER return rate may be even higher because researchers only examined a single “safety-net” hospital in Boston, the researchers announced in the Annals of Emergency Medicine.

“Hospital readmissions within 30 days of inpatient discharge are frequent and costly,” study author Kristin Rising, MD, was quoted as saying in ScienceDaily. Almost half of the ER visits studied—46 percent—resulted in the patients being readmitted to the hospital, Rising and her colleagues said.

Last year, some 200 hospitals were fined for failing to cut down on readmissions. But Rising says that current readmission metrics “are missing a large part of the picture since they only include inpatient-to-inpatient hospitalization and ignore return visits to the emergency department that do not result in admissions. Even worse, safety-net hospitals are more likely to draw the uninsured, as well as Medicare and Medicaid patients, Rising said.

The American Health Care Association (AHCA) and other long term care advocates have said consistently that nursing homes can play a key role in reducing readmissions. Earlier this month, AHCA reported that nearly one-quarter of its members had already met the association’s goal of reducing readmissions by 15 percent.

The main culprit in the ER returns and the readmissions was congestive heart failure, Rising and her colleagues said. Diabetes, complications from devices, and pneumonia were the other lead factors in bringing patients back to the ER, while device complications, sickle cell anemia, and abdominal pain were the most likely symptoms to lead to rehospitalizations, Rising and her colleagues wrote.

“These findings indicated that initiatives to address recurrent hospital use may need to vary, depending on the types of recurrent visits being targeted,” Rising said.