Administrative algorithms with optimal combinations of International Classification of Diseases (ICD) codes, provider specialty, diagnostic testing, and exclusion of other interstitial lung disease (ILD) causes accurately classify ILD in rheumatoid arthritis (RA), a new study found. Participants in a large, RA registry were screened for ILD using ICD codes. ICD and procedure codes, provider specialty, and dates were extracted from Veterans Affairs administrative data to construct ILD algorithms. Among the details:

• Medical records of 536 patients with RA were reviewed, confirming 182 (stringent definition) and 203 (relaxed definition) ILD cases.
• Algorithms that included a pulmonologist diagnosis or chest CT plus pulmonary function testing or lung biopsy had improved performance.
• Positive predictive value (PPV) increased with exclusion of other ILD causes in comparisons with the relaxed ILD definition and in sensitivity analyses.
• Gains in specificity and PPV with greater algorithm requirements were accompanied by declines in sensitivity.