International Classification of Diseases (ICD) Codes for Congenital Heart Defects (CHD) Have Variable and Limited Accuracy for Detecting CHD Cases

ABSTRACT Background Administrative data permits analysis of large cohorts but relies on International Classification of Diseases, Ninth and Tenth Revision, Clinical Modification (ICD) codes that may not reflect true congenital heart defects (CHD). Methods 1497 cases with at least one encounter between 1/1/2010 – 12/31/2019 in two healthcare systems (one adult, one pediatric) identified by at least one of 87 ICD CHD codes were validated through chart review for the presence of CHD and CHD anatomic group. Results Inter- and intra-observer reliability averaged > 95%. Positive predictive value (PPV) of ICD codes for CHD was 68.1% (1020/1497) overall, 94.6% (123/130) for cases identified in both healthcare systems, 95.8% (249/260) for severe codes, 52.6% (370/703) for shunt codes, 75.9% (243/320) for valve codes, 73.5% (119/162) for shunt and valve codes, and 75.0% (39/52) for “Other CHD” (7 ICD codes). PPV for cases with >1 unique CHD code was 85.4% (503/589) vs. 56.3% (498/884) for one CHD code. Of cases with secundum atrial septal defect ICD codes 745.5/Q21.1 in isolation, 30.9% (123/398) had a confirmed CHD. Patent foramen ovale was present in 66.2% (316/477) of false positives (FP). The median number of unique CHD-coded encounters was higher for true positives (TP) than FP (2.0; interquartile range [IQR]: 1.0-3.0 vs 1.0; IQR:1.0-1.0, respectively, p<0.0001). TP had younger mean age at first encounter with a CHD code than FP (22.4 years vs 26.3 years, p=0.0017). Conclusion PPV of CHD ICD codes varies by characteristics for detection of CHD by ICD code and anatomic grouping. While an ICD code for severe CHD and/or the presence of a case in more than one data source, regardless of anatomic group, is associated with higher PPV for CHD, most TP cases did not have these characteristics. The development of algorithms to improve accuracy may improve administrative data for CHD surveillance.