Rheumatology International

, Volume 38, Issue 6, pp 1083–1088 | Cite as

Pseudogout among Patients Fulfilling a Billing Code Algorithm for Calcium Pyrophosphate Deposition Disease

  • Sara K. Tedeschi
  • Daniel H. Solomon
  • Katherine P. Liao
Observational Research


To test the performance of a billing claims-based calcium pyrophosphate deposition disease (CPPD) algorithm for identifying pseudogout. We applied a published CPPD algorithm at an academic institution and randomly selected 100 patients for electronic medical record review for 3 phenotypes: (1) definite/probable CPPD, (2) definite/probable pseudogout; (3) definite pseudogout. Clinical data were recorded and positive predictive value (PPV) (95% CI) for each phenotype was calculated. We then modified the published algorithm to require ≥ 1 of 4 relevant terms (“pseudogout”, “calcium pyrophosphate crystals”, “CPPD”, or “chondrocalcinosis”) through automated text searching in clinical notes, and re-calculated PPVs. To estimate the percentage of pseudogout patients not identified by the published algorithm, we reviewed a random sample of 50 patients with ≥ 1 of 4 relevant terms in clinical notes who did not fulfill the published algorithm. Among patients fulfilling the published algorithm, 68% had ≥ 1 of 3 phenotypes. The published algorithm had PPV 24.0% (95% CI 19.3–28.7%) for definite/probable pseudogout and 18.0% (95% CI 14.5–21.5%) for definite pseudogout. Requiring ≥ 1 of 4 relevant terms in clinical notes increased PPV to 33.3% (95% CI 26.8–39.8%) for definite/probable pseudogout and 24.6% (95% CI 19.8–29.4%) for definite pseudogout. Among patients not fulfilling the published algorithm, 16.0% had definite/probable pseudogout and 6.0% had definite pseudogout. A billing code-based CPPD algorithm had low PPV for identifying pseudogout. Adding text searching modestly enhanced the PPV, though it remained low. These findings highlight the need for improved approaches to identify pseudogout to facilitate epidemiologic studies.


Pseudogout Calcium pyrophosphate CPPD Algorithm 


Author contributions

SKT collected and analyzed electronic medical record data, interpreted results, and was a major contributor to the manuscript. DHS and KPL contributed to study design, interpretation of results, and manuscript preparation. All authors read and approved the final manuscript.


This work was supported by the National Institute of Arthritis and Musculoskeletal and Skin Diseases at the National Institutes of Health [L30 AR070514, K24 AR055989, and P30 AR072577]. The funding source had no rule in study design or collection, analysis and interpretation of the data or manuscript preparation.

Compliance with ethical standards

Conflict of interest

Dr. Tedeschi, Dr. Solomon, and Dr. Liao declare that they have no conflict of interest.

Ethical approval

For this type of study formal consent is not required.


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Copyright information

© Springer-Verlag GmbH Germany, part of Springer Nature 2018

Authors and Affiliations

  1. 1.Division of Rheumatology, Immunology and AllergyBrigham and Women’s HospitalBostonUSA

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