The validity of International Classification of Diseases, Ninth Revision, Clinical Modification diagnosis codes for identifying patients hospitalized for COPD exacerbations.

BACKGROUND: Acute exacerbations of COPD (AE-COPD) are a leading cause of hospitalizations in the United States. To estimate the burden of disease (eg, prevalence and cost), identify opportunities to improve care quality (eg, performance measures), and conduct observational comparative effectiveness research studies, various algorithms based on the International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM) codes have been used to identify patients with COPD. However, the validity of these algorithms remains unclear. METHODS: We compared the test characteristics (sensitivity, specificity, positive predictive value, and negative predictive value) of four different coding algorithms for identifying patients hospitalized for an exacerbation of COPD with chart review (reference standard) using a stratified probability sample of 200 hospitalizations at two urban academic medical centers. Sampling weights were used when calculating prevalence and test characteristics. RESULTS: The prevalence of COPD exacerbations (based on the reference standard) was 7.9% of all hospitalizations. The sensitivity of all ICD-9-CM algorithms was very low and varied by algorithm (12%-25%), but the negative predictive value was similarly high across algorithms (93%-94%). The specificity was > 99% for all algorithms, but the positive predictive value varied by algorithm (81%-97%). CONCLUSIONS: Algorithms based on ICD-9-CM codes will undercount hospitalizations for AE-COPD, and as many as one in five patients identified by these algorithms may be misidentified as having a COPD exacerbation. These findings suggest that relying on ICD-9-CM codes alone to identify patients hospitalized for AE-COPD may be problematic.

Hospitalizations for acute exacerbations of chronic obstructive pulmonary disease: how you count matters.

ICD-9-CM diagnosis codes are increasingly used to estimate the burden of disease, as well as to evaluate the quality of care and outcomes of various conditions. Acute exacerbations of COPD (AE-COPD) are common and associated with substantial health and financial burden in the U.S. Whether published algorithms that employ different combinations of ICD-9-CM codes to identify patients hospitalized for AE-COPD yield similar or different estimates of disease burden is unclear. In this study, the Nationwide Inpatient Sample from years 2000-2006 was used to identify and compare the number of hospitalizations, healthcare utilization, and outcomes for patients hospitalized for AE-COPD in the U.S. AE-COPD was identified using five different published ICD-9-CM algorithms. Estimates of the annual number of hospitalizations for AE-COPD in the U.S. varied more than 2-fold (e.g., 421,000 to 870,000 in 2006). Outcomes and healthcare utilization of patients hospitalized for AE-COPD varied substantially, depending on the algorithm used (e.g., in-hospital mortality 2.0% to 5.1%, total hospital days 2.0 to 5.1 million in 2006). Observed trends in the number of hospitalizations over the 7-year period varied depending on which algorithm was used. In conclusion, the estimated health burden and trends in hospitalizations for AE-COPD in the United States differ, depending on which ICD-9-CM algorithm is used. To improve our understanding of the burden of AE-COPD and to ensure that quality of care initiatives are not misdirected, a validated approach to identifying patients hospitalized for AE-COPD is needed.