Myocardial Injury Often Miscoded as Type 2 MI
The study authors say coding errors have implications for value-based care and could affect the accuracy of research that relies on billing data.
Many patients with nonischemic myocardial injury may be misclassified in hospital billing codes as having type 2 MI (T2MI), a new study shows.
Senior author Jason H. Wasfy, MD, MPhil (Massachusetts General Hospital and Harvard Medical School, Boston, MA), told TCTMD that while he expected at the outset to see some misclassification of patients with myocardial injury, he was surprised by the large number his group found.
“It was pretty alarming that in nearly half the cases it was not classified correctly,” he said. Of 633 patients coded as having T2MI in the study, strict adjudication later showed that 41.9% actually had myocardial injury.
“The problem is that we use claims data for research to try to improve quality of care. We also use these data to push forward payment reform,” Wasfy noted. “Conceptually, we would love to get to the point where hospitals and doctors are paid in part based on meaningful quality measures, but time and time again we find that when you use claims data to assess the quality of care, it's very difficult to understand what’s going on.”
The study, led by Cian McCarthy, MB, BCh (Massachusetts General Hospital), was presented recently at the American College of Cardiology 2019 Scientific Session and simultaneously published in JAMA Cardiology.
For adjudication purposes, myocardial injury was defined by a cardiac troponin T concentration of ≥ 0.03 ng/mL, or a fifth-generation high-sensitivity troponin T concentration of ≥ 10 ng/L for women or ≥ 15 ng/L for men. MI was defined as a rising or falling elevation in cardiac troponin more than the 99th percentile and symptoms of ischemia, new electrocardiographic evidence of ischemia, new pathological Q waves, new regional wall motions on imaging in an ischemic territory, or coronary thrombus on angiography. T2MI was defined as an MI with an identifiable preceding imbalance between myocardial oxygen supply and demand that was not associated with coronary thrombus.
Patients with T2MI and those with myocardial injury had similar rates of in-hospital all-cause mortality, cardiovascular mortality, recurrent MI, and stroke, and a similar median length of stay. Among those who survived to discharge, both 30-day readmission rates and 30-day mortality rates were comparable between T2MI and myocardial injury patients.
Data Assessment and Quality of Care at Issue
Wasfy said the findings may reflect confusion among clinicians because the guidelines for classifying T2MI and myocardial injury are complex, as well as simple lack of time.
"Our first duty is obviously to the patient, not sorting out these subtle differences in billing codes,” Wasfy noted. “I do think we have a duty to do our best to try to click the right codes, but it’s often very complicated if the clinical situation doesn't fit the choices that you have."
The impact of miscoding on value-based programs could be considerable, the researchers observe. “For instance, the Hospital Value-Based Purchasing Program creates an incentive payment fund by reducing inpatient Medicare payments by 2% and then distributes the fund to hospitals by applying a value-based adjustment factor that is determined by the hospital’s total performance score (which includes inpatient mortality rates for MI),” they write. “Based on performance levels, some hospitals will earn less than the 2% back, resulting in a ‘penalty,’ while other hospitals will earn more than 2% back and receive a ‘bonus.’” Recent research, they add, has shown that many T2MI patients are included in Hospital Readmission Reduction Program penalties.
Wasfy acknowledged that the problem is complicated and will take time to sort out. He said his institution intends to work on how best to address the issue they’ve identified, and while physician education about definitions and classifications is part of the problem, he thinks more information also is needed on how the codes that clinicians click are being translated into claims data and how those data ultimately are being used.
“What this [study] shows you is that claims data is not reliable for assessment of quality of care,” he concluded.
McCarthy C, Murphy S, Cohen JA, et al. Misclassification of myocardial injury as myocardial infarction: implications for assessing outcomes in value-based programs. JAMA Cardiol. 2019;Epub ahead of print.
- McCarthy reports no relevant conflicts of interest.
- Wasfy report receiving grants from the American Heart Association, the National Institutes of Health, and Harvard Catalyst during the conduct of the study.