Validation of the Abdominal Pain Index using a revised scoring method.
OBJECTIVE
Evaluate the psychometric properties of child- and parent-report versions of the four-item Abdominal Pain Index (API) in children with functional abdominal pain (FAP) and healthy controls, using a revised scoring method that facilitates comparisons of scores across samples and time.


METHODS
Pediatric patients aged 8-18 years with FAP and controls completed the API at baseline (N = 1,967); a subset of their parents (N = 290) completed the API regarding the child's pain. Subsets of patients completed follow-up assessments at 2 weeks (N = 231), 3 months (N = 330), and 6 months (N = 107). Subsets of both patients (N = 389) and healthy controls (N = 172) completed a long-term follow-up assessment (mean age at follow-up = 20.21 years, SD = 3.75).


RESULTS
The API demonstrated good concurrent, discriminant, and construct validity, as well as good internal consistency.


CONCLUSION
We conclude that the API, using the revised scoring method, is a useful, reliable, and valid measure of abdominal pain severity.