Objective: To assess the accuracy of International Classification of Diseases, 9th Revision, Clinical Modification (ICD-9-CM), codes in identifying cases of child physical abuse in 4 children's hospitals.

Methods: We included all children evaluated by a child abuse pediatrician (CAP) for suspicion of abuse at 4 children's hospitals from January 1, 2007, to December 31, 2010. Subjects included both patients judged to have injuries from abuse and those judged to have injuries from accidents or to have medical problems. The ICD-9-CM codes entered in the hospital discharge database for each child were compared to the decisions made by the CAPs on the likelihood of abuse. Sensitivity and specificity were calculated. Medical records for discordant cases were abstracted and reviewed to assess factors contributing to coding discrepancies.

Results: Of 936 cases of suspected physical abuse, 65.8% occurred in children <1 year of age. CAPs rated 32.7% as abuse, 18.2% as unknown cause, and 49.1% as accident/medical cause. Sensitivity and specificity of ICD-9-CM codes for abuse were 73.5% (95% confidence interval 68.2, 78.4), and 92.4% (95% confidence interval 90.0, 94.0), respectively. Among hospitals, sensitivity ranged from 53.8% to 83.8% and specificity from 85.4% to 100%. Analysis of discordant cases revealed variations in coding practices and physicians' notations among hospitals that contributed to differences in sensitivity and specificity of ICD-9-CM codes in child physical abuse.

Conclusions: Overall, the sensitivity and specificity of ICD-9-CM codes in identifying cases of child physical abuse were relatively low, suggesting both an under- and overcounting of abuse cases.