Validation of diagnostic coding for chronic obstructive pulmonary disease in an electronic health record system in Hong Kong.

Introduction: Electronic health record databases can facilitate epidemiology research regarding diseases such as chronic obstructive pulmonary disease (COPD), a common medical condition worldwide. We aimed to assess the validity of International Classification of Diseases, 9th Revision (ICD-9) code algorithms for identifying COPD in Hong Kong's territory-wide electronic health record system, the Clinical Data Analysis and Reporting System (CDARS).

Methods: Adult patients diagnosed with COPD at all public hospitals in Hong Kong and specifically at Queen Mary Hospital from 2011 to 2020 were identified using the ICD-9 code 496 (Chronic airway obstruction, not elsewhere classified) within the CDARS. Two respiratory specialists reviewed clinical records and spirometry results to confirm the presence of COPD in a randomly selected group of cases.

Results: During the study period, 93 971 and 2479 patients had the diagnostic code for COPD at all public hospitals in Hong Kong and specifically at Queen Mary Hospital, respectively. Two hundred cases were randomly selected from Queen Mary Hospital for validation using medical records and spirometry results. The overall positive predictive value was 81.5% (95% confidence interval=76.1%-86.9%). We also developed an algorithm to identify COPD cases in our cohort.

Conclusion: This study represents the first validation of ICD-9 coding for COPD in the CDARS. Our findings demonstrated that the ICD-9 code 496 is a reliable indicator for identifying COPD cases, supporting the use of the CDARS database for further clinical research concerning COPD.