Objective: To study the accuracy of diagnoses of spondylarthritides in computerized databases at the Minneapolis Veterans Affairs Medical Center.
Methods: Medical records were available and reviewed for a random sample of 184 patients from a cohort of 737 patients seen at the rheumatology clinic between January 1, 2001 and July 31, 2002. We compared 4 database definitions with the medical record gold standard of rheumatologists' diagnosis of ankylosing spondylitis (AS), psoriatic arthritis (PsA), or reactive arthritis (ReA): presence of 1) > or =1 or 2) > or =2 International Classification of Diseases, Ninth Revision (ICD-9) diagnostic codes for diagnoses of AS (720.0), PsA (696.0), and ReA (099.3, 711.11-711.19), and presence of 3) > or =1 or 4) > or =2 ICD-9 codes and prescription of a disease-modifying antirheumatic drug (DMARD). Accuracy was assessed by sensitivity, specificity, positive predictive values (PPVs) and negative predictive values (NPVs), kappa statistic, and receiver operator characteristic (ROC) curve area.
Results: Of 184 patients, 11 (6%) had AS, 17 (9%) had PsA, and 7 (4%) had ReA as per the gold standard. ICD-9 codes for AS, PsA, and ReA were very specific (98-100%) with excellent NPV (99-100%) and PPV (83-100%), good to excellent sensitivity (57-100%), almost perfect kappa agreement (0.72-1), and high ROC curve area (0.79-1). Addition of presence of DMARD prescription to ICD-9 codes of AS and PsA decreased sensitivity to 27-65% without improving the specificity (which was already high at 99-100%).
Conclusion: The ICD-9 codes for AS, PsA, and ReA in databases are accurate. ICD-9 codes may be used to identify cohorts of patients with spondylarthritides.