Validation of Administrative Codes for Calcium Pyrophosphate Deposition A Veterans Administration Study

Background: Despite high prevalence, progress in calcium pyrophosphate deposition (CPPD) has been limited by poor awareness and absence of validated approaches to study it in large data sets. Objectives: We aimed to determine the accuracy of administrative codes for the diagnosis of CPPD as a foundational step for future studies. Methods: We identified all patients with an International Classification of Diseases, Ninth Revision, Clinical Modification code for chondrocalcinosis (712.1-712.39) or pseudogout/other disorders of mineral metabolism (275.49), and convenience sample selected a comparison group with gout (274.00-03 or 274.8-9), or rheumatoid arthritis (714.0) from 2009 to 2011 at a Veterans Affairs medical center. Each patient was categorized as having definite, probable, or possible CPPD or absence of CPPD based on the McCarty and Ryan criteria using chart abstracted data including crystal analysis, radiographs, and arthritis history. Results: Two hundred forty-nine patients met the clinical gold standard criteria for CPPD based on medical records, whereas 48 patients met definite criteria, 183 probable, and 18 met possible criteria. The accuracy of administrative claims with a code of 712 or 275.49 for definite or probable CPPD was as follows: 98% sensitivity (95% confidence interval, 96%-99%), 78% specificity (74%-83%), 91% positive predictive value, and 94% negative predictive value. Conclusions: At this center, single administrative code 275.49 or 712 accurately identifies patients with CPPD with a positive predictive value of 91%. These findings suggest that administrative codes can have strong clinical accuracy and merit further validation to allow adoption in future epidemiologic studies of CPPD.