To evaluate diagnostic properties of International Classification of Diseases, Version 9 (ICD-9) diagnosis codes and infection criteria to identify bacterial infections among rheumatoid arthritis (RA) patients.
We performed a cross-sectional study of RA patients with and without ICD-9 codes for bacterial infections. Sixteen bacterial infection criteria were developed. Diagnostic properties of comprehensive and restrictive sets of ICD-9 codes and the infection criteria were tested against an adjudicated review of medical records.
Records on 162 RA patients with and 50 without purported bacterial infections were reviewed. Positive and negative predictive values of ICD-9 codes ranged from 54%-85% and 84%-100%, respectively. Positive predictive values of the medical records based criteria were 84% and 89% for "definite" and "definite or empirically treated" infections, respectively. Positive predictive value of infection criteria increased by 50% as disease prevalence increased using ICD-9 codes to enhance infection likelihood.
ICD-9 codes alone may misclassify bacterial infections in hospitalized RA patients. Misclassification varies with the specificity of the codes used and strength of evidence required to confirm infections. Combining ICD-9 codes with infection criteria identified infections with greatest accuracy. Novel infection criteria may limit the requirement to review medical records.