ICD-10 codes for surveillance of non-fatal abusive head trauma in Aotearoa New Zealand: a retrospective cohort study

OBJECTIVES: To assess the validity of an International Classification of Diseases (ICD) code based definition of non-fatal head trauma caused by child abuse (abusive head trauma) for population surveillance in New Zealand. DESIGN: A retrospective cohort study of hospital inpatient records. SETTING: A tertiary children’s hospital in Auckland, New Zealand. PARTICIPANTS: 1731 children less than 5 years of age who were discharged after a non-fatal head trauma event over a 10-year period from 1 January 2010 to 31 December 2019. OUTCOME MEASURES: The outcome of assessment by the hospital’s multidisciplinary child protection team (CPT) was compared with the outcome of ICD, Tenth Revision (ICD-10) discharge coding for non-fatal abusive head trauma (AHT). The ICD-10 code definition of AHT was derived from an ICD, Ninth Revision, Clinical Modification definition developed by the Centers for Disease Control, Atlanta, Georgia, which requires both a clinical diagnosis code and a cause-of-injury code. RESULTS: There were 1755 head trauma events with 117 determined as AHT by the CPT. The ICD-10 code definition had a sensitivity of 66.7% (95% CI 57.4 to 75.1) and specificity of 99.8% (95% CI 99.5 to 100). There were only three false positives but 39 false negatives, with 18 of the false negatives coded with X59 (exposure to unspecified factor). CONCLUSIONS: The ICD-10 code broad definition of AHT is a reasonable epidemiological tool for passive surveillance of AHT in New Zealand but it underestimates the incidence. Its performance could be improved by clear documentation of child protection conclusions in clinical notes, clarifying coding practice and removing the exclusion criteria from the definition.