Acute Care/Hospitalization

Diagnostic codes alone may misclassify bacterial infections among hospitalized patients with rheumatoid arthritis

Bacterial infections are common among patients suffering from rheumatoid arthritis (RA). However, RA patients receiving biologic therapies are reporting a growing number of serious infections. Therefore, it is important not to misclassify infections and thus mask the risks related to use of particular arthritis medications, caution the authors of a new study. They found that diagnostic (ICD-9) codes alone may misclassify bacterial infections in hospitalized RA patients, although the level of misclassification varied depending on the codes used and the strength of evidence required to confirm these infections. Combining ICD-9 codes with validated medical records-based infection criteria identified infections with the greatest accuracy.

The researchers at the Center for Education and Research on Therapeutics (CERT) of Musculoskeletal Disorders, University of Alabama at Birmingham, reviewed the medical records of 162 RA patients with and 50 RA patients without any ICD-9 code(s) for bacterial infection. Positive and negative predictive values (probability that disease is really present when the test is positive or not present when the test is negative) of ICD-9 codes ranged from 54 to 85 percent and 84 to 100 percent, respectively. Positive predictive values of the medical records-based criteria were 84 and 89 percent for "definite" and "definite or empirically treated infections," respectively. The positive predictive value of infection criteria increased by 50 percent as disease prevalence increased, using ICD-9 codes to enhance the likelihood of identifying infections.

The study was supported in part by the Agency for Healthcare Research and Quality by a grant (HS10389) to the University of Alabama at Birmingham CERT of Musculoskeletal Disorders. For more information on the CERTs program, visit http://certs.hhs.gov/index.html.

More details are in "Administrative codes combined with medical records based criteria accurately identified bacterial infections among rheumatoid arthritis patients," by Nivedita M. Patkar, M.D., M.P.S.H., Jeffrey R. Curtis, M.D., M.P.H., Gim Gee Teng, M.D., M.B.B.S., and others, in the Journal of Clinical Epidemiology 69, pp. 321-327, 2009.

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