In the United States, stroke is one of the leading causes of death, disability, hospitalizations, and health care costs. Now, researchers have found that including stroke severity data in hospital mortality risk models allows physicians to better predict the 30-day mortality risk among patients with acute ischemic stroke.
The study, conducted by Gregg C. Fonarow, M.D., of the University of California, Los Angeles, and his team, is published in the July 18 issue of JAMA.
The researchers explained:
“Increasing attention has been given to defining the quality and value of health care through reporting of process and outcome measures. National quality profiling efforts have begun to report hospital-level performance for Medicare beneficiaries, including 30-day mortality rates, for common medical conditions, including acute myocardial infarction [heart attack], heart failure, and community-acquired pneumonia.
There is increasing interest in reporting risk-standardized outcomes for Medicare beneficiaries hospitalized with acute ischemic stroke, but whether it is necessary to include adjustment for initial stroke severity has not been well studied.”
The team conducted the study in order to determine how much hospital outcome ratings and the ability to predict 30-day mortality are changed after adding initial stroke severity in a claims-based risk model for hospital 30-day mortality for acute ischemic stroke.
The researcher analyzed data from 782 hospitals on 127,950 fee-for-service Medicare beneficiaries with ischemic stroke. 86% of patients were white, 57% were women, and the median age of patients was 80 years.
Each patient had a score recorded for the National Institutes of Health Stroke Scale (NIHSS). The score scale ranged from 0 to 42, with higher scores indicating more severe stroke.
In order to assess 30-day mortality the researchers evaluated performance of claims-based mortality risk models with and without inclusion of NIHSS scores. In addition, hospital rankings from both models were compared.
According to the researchers, 18,186 deaths occurred with the first 30 days, of which 7,430 occurred in-hospital. In addition, they found that the median hospital-level 30-day mortality rate was 14.5%.
The researchers found that the hospital mortality model which included NIHSS scores was significantly better at predicting mortality rates than the model without NIHSS scores.
Furthermore, they found that more than 40% of hospitals identified in either the top of bottom 5% of hospital risk-adjusted mortality would have been reclassified into the middle mortality range using a model adjusting for NIHSS score.
The researchers explained: “Similarly, when considering the top 20 percent and bottom 20 percent ranked hospitals, close to one-third of hospitals would have been reclassified.”
They continue: “These findings highlight the importance of including a valid specific measure of stroke severity in hospital risk models for mortality after acute ischemic stroke for Medicare beneficiaries. Furthermore, this study suggests that inclusion of admission stroke severity may be essential for optimal ranking of hospital with respect to 30-day mortality.
As public reporting and value-based purchasing policies increase for outcome measures, it is important to recognize the effect that using models with less than ideal discrimination and calibration has on the ranking of hospitals and the lack of correlation among ranking by models that do and do not adjust for critical risk determinants.”
In an associated report, Tobias Kurth, M.D., Sc.D., of the University of Bordeaux, France, and Mitchell S. V. Elkind, M.D., M.S., of Columbia University, New York, state that the study results:
“Clearly highlight the importance of incorporating information on stroke severity when conducting health outcomes research in stroke. Excluding this information will lead to incorrect ranking of hospital performance by failing to consider that hospitals care for different patient populations. The influence of stroke severity on these outcome measures, moreover, seems different from that of measures of severity in other conditions.
For other cardiovascular diseases, risk adjustment using demographic characteristics and claims-derived comorbid conditions may sufficiently account for the underlying case mix. Ischemic stroke is a much more heterogeneous condition than ischemic heart disease and is characterized by multiple subtypes, etiologies, and diverse outcomes.
The assumption that what is true of myocardial infarction is also true of stroke, therefore, is flawed, as the present data underscore. The particular characteristics of stroke have to be taken into consideration by clinicians, insurance companies, and policy makers when comparing disease-specific health outcomes.”
Written by Grace Rattue