In addition to reflecting poorly on a hospital's quality of care, a high readmission rate also can result in reduced Medicare reimbursements, under provisions taking effect under a 2010 health care law.

But a study of spine surgery patients has found that the standard method used to calculate readmission rates can be a misleading indicator of hospital quality. Loyola University (Chicago) Medical Center neurosurgeon Dr. Beejal Amin and colleagues found that 25 percent of the readmissions of spine surgery patients weren't due to true quality-of-care issues.

Amin presented findings earlier this month at the 2012 meeting of the Congress of Neurological Surgeons in Chicago. He earlier presented findings at the 2012 meeting of the American Association of Neurological Surgeons.

"We have identified potential pitfalls in the current calculation of readmission rates," Amin says. "We are working on modifying the algorithm to make it more clinically relevant."

Medicare is trying to improve patient care by penalizing hospitals with poor outcomes. One key outcome measure is readmissions rate. On Oct. 1, Medicare began fining hospitals that have too many patients readmitted within 30 days.

In spine surgery, a high readmission rate can indeed reflect poorly on a hospital's quality of care if the readmissions are due to infections, surgical complications, blood clots, or failures of surgical hardware, Amin says.

But some types of readmissions aren't a true indication of quality of care, he says. Such cases include planned readmission for a staged procedure, such as a procedure to straighten a curved spine in a scoliosis patient, which requires two surgeries performed about 15 days apart.

In some cases, readmission can be unrelated to spine surgery. Occasionally, patients who undergo spine surgery will be readmitted within 30 days for surgery for an unrelated condition, such as a hip replacement.

Also, operations sometimes are canceled or rescheduled for unpreventable reasons. For example, a patient is admitted to the hospital but the spinal surgery is postponed due to an irregular heart rate. The patient is readmitted a couple weeks later for elective surgery, after the heart rhythm is controlled.

Amin and colleagues examined the records of 5,780 spine surgery patients treated at the University of California San Francisco Medical Center between October 2007 and June 2011. Before recently joining Loyola, Amin did a clinical fellowship in complex spine surgery at UCSF. He now is an assistant professor in the Department of Neurological Surgery at Loyola University Chicago Stritch School of Medicine. His clinical expertise is in minimally invasive spine surgery.

The study found that, under the standard readmission formula, 281 patients were readmitted within 30 days of discharge. But 69 of these readmissions, or 25 percent, shouldn't have been counted against the hospital. These included 39 cases that were planned readmissions for staged procedures, 16 cases that were unrelated to spine surgery, and 14 cases that were canceled or rescheduled due to unpreventable reasons. Thus, the current method used to calculate readmissions overstated the true spine surgery-related readmissions by 25 percent.

"Our analysis identified potential pitfalls in the current calculation of readmission rates and highlights the need for defining a clinically relevant algorithm that accurately calculates readmission rates in spine surgery," Amin says. "Readmissions should be determined not only by hospital readmission, but also require the presence of a diagnosis code that indicates a spine-related complication. This will help prevent false positive readmission classification."