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Development and Validation of a Simple Risk Score

Ying P. Tabak, PhD; Xiaowu Sun, PhD; Richard S. Johannes, MD, MS; Vikas Gupta, PharmD; Andrew F. Shorr, MD, MPH

Arch Intern Med. 2009;169(17):1595-1602.

Background  Acute exacerbations of chronic obstructive pulmonary disease (AECOPDs) often require hospitalization, may necessitate mechanical ventilation, and can be fatal. We sought to develop a simple risk score to determine its severity.

Methods  We analyzed 88 074 subjects admitted with an AECOPD between 2004 and 2006. We used recursive partition to create risk classifications for in-hospital mortality. Need for mechanical ventilation served as a secondary end point. We internally validated the model via 1000 bootstrapping on half of patients and externally validated it on the remaining patients. We assessed predictive ability using the area under the receiver operating curve (AUROC).

Results  The in-hospital mortality rate was 2%. Three variables had high discrimination of outcomes: serum urea nitrogen level greater than 25 mg/dL (to convert to millimoles per liter, multiply by 0.357); acute mental status change, and pulse greater than 109/min. For those without any of the 3 factors, age 65 years or younger further differentiated the lowest-risk group. In those with all 3 factors, the mortality rates were 13.1% (131 in 1000) and 14.6% (146 in 1000) in the derivation and validation cohorts, respectively, compared with 0.3% (3 in 1000) in both cohorts among patients without any of the 3 factors and age 65 years or younger (P < .001). The AUROC for mortality in the 2 cohorts were 0.72 (95% confidence interval [CI], 0.70-0.74) and 0.71 (95% CI, 0.70-0.73), respectively. For mechanical ventilation, the AUROCs were 0.77 (95% CI, 0.75-0.79) for both cohorts.

Conclusions  A simple risk class based on clinical variables easily obtained at presentation predicts mortality and need for mechanical ventilation. It may facilitate the triage and care of patients with AECOPD.

Author Affiliations: Clinical Research Services, Cardinal Health, Marlborough, Massachusetts (Drs Tabak, Sun, Johannes, and Gupta); Division of Gastroenterology, Department of Medicine, Harvard Medical School, Boston, Massachusetts (Dr Johannes); and Pulmonary and Critical Care Medicine, Washington Hospital Center, Washington, DC (Dr Shorr).

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In This Issue of Archives of Internal Medicine
Arch Intern Med. 2009;169(17):1550.
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