Chronic Disease

Diagnostic coding formulas underestimate hospitalizations for acute exacerbations of COPD

Individuals with chronic obstructive pulmonary disease (COPD) often suffer from acute exacerbations over the course of the disease. The resulting hospitalizations cost nearly $30 billion annually and 120,000 people die each year. Various algorithms based on ICD-9-CM discharge diagnosis codes are used to identify patients with COPD exacerbations. However, a new study finds that such algorithms are not accurate at identifying patients hospitalized with COPD exacerbations. What's more, they misidentify other patients as having a COPD exacerbation.
Four algorithms using ICD-9-CM codes were evaluated in the study of 200 adults admitted at two academic medical centers. These adults were hospitalized with and without acute exacerbations of COPD. The researchers also looked at patient demographics, length of stay, and mortality outcomes. A total of 8,790 patients met eligibility criteria. Overall, 7.9 percent of patients, or 1 in 13, were hospitalized for acute exacerbations of COPD. All four algorithms had very low sensitivity when it came to identifying these patients, ranging from 12 to 25 percent. As a result, hospitalizations for acute exacerbations of COPD were undercounted. The two algorithms that used a combination of primary and secondary discharge codes demonstrated the highest sensitivity. All of the algorithms had a similarly high negative predictive value of 93 to 94 percent. Depending on the algorithm used to identify exacerbations, as many as 1 in 5 patients were mistakenly identified as having a COPD exacerbation.
Out of the four algorithms, the researchers suggest using one that relies on a single primary code specifically for acute-exacerbation COPD when conducting quality improvement initiatives. The study was supported by the Agency for Healthcare Research and Quality (HS16967).
See "The validity of International Classification of Diseases, Ninth Revision, clinical modification diagnosis codes for identifying patients hospitalized for COPD exacerbations," by Brian D. Stein, M.D., Adriana Bautista, M.D., Glen T. Schumock, Pharm.D., and others in the January 2012 Chest 141(1), pp. 87-93.

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