Administrative codes combined with medical records based criteria accurately identified bacterial infections among rheumatoid arthritis patients

Abstract

Objective: 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.

Study design and setting: 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.

Results: 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.

Conclusion: 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.

Figure 1

Selection of rheumatoid arthritis (RA) patient population for assessing diagnostic properties of ICD-9^* codes and medical records-based infection criteria for serious bacterial infections. ^* ICD-9, International Classification of Diseases, Version 9, Clinical Modification.

Figure 2

Positive predictive value (%) of ICD-9^* codes according to the prevalence of bacterial Infections, the categories of reviewers’ assessment for infection^†, and the groupings^‡ of diagnostic codes (based on extrapolation to full cohort of 557 patients with rheumatoid arthritis). ^* ICD-9, International Classification of Diseases, Version 9, Clinical Modification ^† Category of reviewers’ assessment of medical records for identifying “definite” and “definite or empirically treated” bacterial infections. ^‡ Comprehensive and restricted sets of ICD-9 codes of potential bacterial infections.

Figure 3

Positive Predictive Value (%) of medical records-based infection criteria according to the prevalence of bacterial Infections and the categories of reviewers’ assessment for infection^*. ^*Category of reviewers’ assessment of medical records for identifying “definite” and “definite or empirically treated” bacterial infections.