The results of the Centers for Medicare & Medicaid Services’ program to reduce hospital readmissions are being called into question by two new studies — with one suggesting the initiative may have the “unintended consequence” of raising patient mortality rates.

The first study, published Sunday in JAMA Cardiology, analyzed more than 115,000 Medicare beneficiaries hospitalized with heart failure across the United States. The Harvard Medical School-based team found 30-day readmission rates declined following the implementation of the Hospital Readmissions Reduction Program, from 20% to 18.4%.

The 30-day risk-adjusted mortality rate of patients in the program was shown to increase, from 7.2% before implementation to 8.6% after it. One-year readmission and mortality rates followed a similar pattern, researchers said.

Those results may indicate that the HRRP may have incentivized hospitals to cut readmissions in a way that jeopardized the health and survival of heart failure patients. If confirmed by further research, health officials may need to reconsider the participation of heart failure patients in the program, researchers said.

A second HRRP-related study, published Monday in JAMA Internal Medicine by University of Michigan researchers, indicated the program may have overstated its success in reducing readmissions.

The research team found that 63% of the readmission reductions could be simply attributed to the way patients’ diagnoses were coded, or “how hospitals document the severity of admitted patients.” The number of secondary diagnoses, such as obesity or hypertension in heart attack patients, increased by 39% at hospitals participating in HRRP. For control hospitals, the number of such diagnoses only increased 20%.

“It is possible that hospitals exposed to the HRRP undercoded severity prior to the HRRP, rather than overcoding severity after the program,” said researcher Andrew Ryan, Ph.D. “Nonetheless, there is a long history of healthcare providers and health plans increasing the coded severity of patients when it is to their advantage to do so.”